diff --git a/tests/Models/Reports/Summary_taxes_test.php b/tests/Models/Reports/Summary_taxes_test.php
new file mode 100644
index 000000000..5ea31dc56
--- /dev/null
+++ b/tests/Models/Reports/Summary_taxes_test.php
@@ -0,0 +1,218 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Models\Reports;
+
+use CodeIgniter\Test\CIUnitTestCase;
+
+class Summary_taxes_test extends CIUnitTestCase
+{
+    public function testRowTotalsAddUp(): void
+    {
+        $rows = [
+            ['subtotal' => 100.00, 'tax' => 10.00, 'total' => 110.00],
+            ['subtotal' => 200.00, 'tax' => 20.00, 'total' => 220.00],
+            ['subtotal' => 50.00, 'tax' => 5.00, 'total' => 55.00],
+        ];
+
+        foreach ($rows as $row) {
+            $calculatedTotal = round((float) $row['subtotal'] + (float) $row['tax'], 2);
+            $this->assertEquals(
+                (float) $row['total'],
+                $calculatedTotal,
+                "Row subtotal + tax should equal total: {$row['subtotal']} + {$row['tax']} = {$row['total']}"
+            );
+        }
+    }
+
+    public function testSummaryTotalsMatchRowSums(): void
+    {
+        $rows = [
+            ['subtotal' => 100.00, 'tax' => 10.00, 'total' => 110.00, 'count' => 5],
+            ['subtotal' => 200.00, 'tax' => 20.00, 'total' => 220.00, 'count' => 10],
+            ['subtotal' => 50.00, 'tax' => 5.00, 'total' => 55.00, 'count' => 3],
+        ];
+
+        $summary = $this->calculateSummary($rows, 2);
+
+        $expectedSubtotal = 0;
+        $expectedTax = 0;
+        $expectedTotal = 0;
+        $expectedCount = 0;
+
+        foreach ($rows as $row) {
+            $expectedSubtotal += (float) $row['subtotal'];
+            $expectedTax += (float) $row['tax'];
+            $expectedTotal += (float) $row['total'];
+            $expectedCount += (int) $row['count'];
+        }
+
+        $this->assertEquals(
+            round($expectedSubtotal, 2),
+            $summary['subtotal'],
+            'Summary subtotal should equal sum of row subtotals'
+        );
+        $this->assertEquals(
+            round($expectedTax, 2),
+            $summary['tax'],
+            'Summary tax should equal sum of row taxes'
+        );
+        $this->assertEquals(
+            round($expectedTotal, 2),
+            $summary['total'],
+            'Summary total should equal sum of row totals'
+        );
+        $this->assertEquals(
+            $expectedCount,
+            $summary['count'],
+            'Summary count should equal sum of row counts'
+        );
+    }
+
+    public function testSubtotalPlusTaxEqualsTotalInSummary(): void
+    {
+        $rows = [
+            ['subtotal' => 100.00, 'tax' => 10.00, 'total' => 110.00, 'count' => 5],
+            ['subtotal' => 200.00, 'tax' => 20.00, 'total' => 220.00, 'count' => 10],
+        ];
+
+        $summary = $this->calculateSummary($rows, 2);
+
+        $calculatedTotal = round($summary['subtotal'] + $summary['tax'], 2);
+        $this->assertEquals(
+            $summary['total'],
+            $calculatedTotal,
+            'Summary subtotal + tax should equal summary total'
+        );
+    }
+
+    public function testRoundingConsistency(): void
+    {
+        $rows = [
+            ['subtotal' => 99.99, 'tax' => 9.999, 'total' => 109.989],
+            ['subtotal' => 33.33, 'tax' => 3.333, 'total' => 36.663],
+        ];
+
+        $summary = $this->calculateSummary($rows, 2);
+
+        $sumOfRoundedSubtotals = 0;
+        $sumOfRoundedTaxes = 0;
+
+        foreach ($rows as $row) {
+            $sumOfRoundedSubtotals += round((float) $row['subtotal'], 2);
+            $sumOfRoundedTaxes += round((float) $row['tax'], 2);
+        }
+
+        $expectedTotal = round($sumOfRoundedSubtotals + $sumOfRoundedTaxes, 2);
+
+        $this->assertEquals(
+            $expectedTotal,
+            $summary['total'],
+            'Total should be sum of rounded subtotals + sum of rounded taxes'
+        );
+    }
+
+    public function testTaxIncludedModeCalculation(): void
+    {
+        $saleAmount = 110.00;
+        $taxAmount = 10.00;
+
+        $subtotal = round($saleAmount - $taxAmount, 2);
+        $total = round($saleAmount, 2);
+
+        $this->assertEquals(100.00, $subtotal, 'Tax-included: subtotal should be sale_amount - tax');
+        $this->assertEquals(110.00, $total, 'Tax-included: total should be sale_amount');
+        $this->assertEquals(
+            $total,
+            round($subtotal + $taxAmount, 2),
+            'Tax-included: total should equal subtotal + tax'
+        );
+    }
+
+    public function testTaxNotIncludedModeCalculation(): void
+    {
+        $saleAmount = 100.00;
+        $taxAmount = 10.00;
+
+        $subtotal = round($saleAmount, 2);
+        $total = round($saleAmount + $taxAmount, 2);
+
+        $this->assertEquals(100.00, $subtotal, 'Tax-not-included: subtotal should be sale_amount');
+        $this->assertEquals(110.00, $total, 'Tax-not-included: total should be sale_amount + tax');
+        $this->assertEquals(
+            $total,
+            round($subtotal + $taxAmount, 2),
+            'Tax-not-included: total should equal subtotal + tax'
+        );
+    }
+
+    public function testNegativeValuesForReturns(): void
+    {
+        $rows = [
+            ['subtotal' => -100.00, 'tax' => -10.00, 'total' => -110.00, 'count' => 1],
+            ['subtotal' => 200.00, 'tax' => 20.00, 'total' => 220.00, 'count' => 2],
+        ];
+
+        foreach ($rows as $row) {
+            $calculatedTotal = round((float) $row['subtotal'] + (float) $row['tax'], 2);
+            $this->assertEquals(
+                (float) $row['total'],
+                $calculatedTotal,
+                "Negative row: subtotal + tax should equal total"
+            );
+        }
+
+        $summary = $this->calculateSummary($rows, 2);
+
+        $this->assertEquals(100.00, $summary['subtotal'], 'Summary should handle negative values');
+        $this->assertEquals(10.00, $summary['tax'], 'Summary tax should handle negative values');
+        $this->assertEquals(110.00, $summary['total'], 'Summary total should handle negative values');
+    }
+
+    public function testZeroTaxRows(): void
+    {
+        $rows = [
+            ['subtotal' => 100.00, 'tax' => 0.00, 'total' => 100.00, 'count' => 1],
+            ['subtotal' => 200.00, 'tax' => 0.00, 'total' => 200.00, 'count' => 2],
+        ];
+
+        foreach ($rows as $row) {
+            $this->assertEquals(
+                (float) $row['subtotal'],
+                (float) $row['total'],
+                'Zero tax: subtotal should equal total'
+            );
+        }
+
+        $summary = $this->calculateSummary($rows, 2);
+
+        $this->assertEquals(
+            $summary['subtotal'],
+            $summary['total'],
+            'Zero tax summary: subtotal should equal total'
+        );
+    }
+
+    private function calculateSummary(array $rows, int $decimals = 2): array
+    {
+        $subtotal = 0;
+        $tax = 0;
+        $total = 0;
+        $count = 0;
+
+        foreach ($rows as $row) {
+            $subtotal += (float) $row['subtotal'];
+            $tax += (float) $row['tax'];
+            $total += (float) $row['total'];
+            $count += (int) $row['count'];
+        }
+
+        return [
+            'subtotal' => round($subtotal, $decimals),
+            'tax' => round($tax, $decimals),
+            'total' => round($total, $decimals),
+            'count' => $count,
+        ];
+    }
+}
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