On one-off invoices, the unit price is limited to 2 decimal places because it's stored/entered as whole cents (unit_amount_cents, integer). Line total is computed as unit_amount_cents × units, rounded. For partial-period / prorated charges, the true per-unit price is often fractional (e.g. $0.1467/unit), so we can't produce a line that hits the exact total while keeping the unit price honest. Current workarounds that are incomplete: Decimal units (e.g. 102.3 units) — hits the exact total, but they read "units sold" off the invoice into their internal reporting, so fractional units corrupt the numbers. Second "proration adjustment" line to carry the remainder. This produces the exact total with clean integer units, but looks weird to end customers.