Repair Money Rounding Bugs

The problem

Binary floating-point math and inconsistent rounding create "off-by-one-cent" errors in invoices, taxes, and refunds. These small discrepancies lead to failed audits, broken payment provider syncs, and reconciliation nightmares.

What it does

• Traces monetary values from input through storage, calculation, and display to find precision loss.
• Establishes a strict Monetary Contract defining rounding modes, currency scales, and calculation stages.
• Replaces unsafe arithmetic with integer minor units or exact decimal types.
• Implements remainder allocation logic to ensure distributed discounts or taxes sum correctly to the total.
• Runs automated reconciliation tests to verify that stored and displayed totals match exactly.

Frameworks & tools

Works with any stack using Read, Edit, and Bash tools. Specifically audits SQL schemas, ORM precision, and payment integrations like Stripe or PayPal.

Why this beats prompting it yourself

General LLMs often suggest simple .toFixed(2) hacks that compound rounding errors. This skill enforces a professional financial engineering workflow, distinguishing between rates, quantities, and amounts while ensuring compliance with currency-specific scales.

Use cases

• Fixing invoice subtotals that do not sum correctly due to line-item rounding.
• Standardizing currency conversion logic across multi-currency databases.
• Repairing "penny-gap" mismatches between your application and payment gateways.
• Auditing tax calculation logic to handle inclusive and exclusive tax rules.

Known limitations

Will not invent tax policies or accounting rules without user evidence. Does not perform destructive migrations on production data without an audit dry-run.