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IEEE 754 floating-point cannot represent base-10 fractions exactly. In JavaScript, 0.1 + 0.2 === 0.30000000000000004. The industry standard for financial software: store all monetary values as integers in the smallest currency unit (cents). Perform all arithmetic on integers. Divide by 100 only for display formatting. This is the approach used by Stripe, Square, and every major payment processor.
