Method and sources
How we calculate
- Every rule comes from the source listed below and is explained on the calculator's page.
- The calculation runs in your browser; the page shows the working with your numbers.
- Results are rounded only when they are displayed.
How we check
- Every rule has test cases with values taken from its source.
- All tests run automatically before each release; if one fails, nothing is published.
- Every number in tables and examples comes from the same code as the calculator.
Sources
| Rule | Source | Verified on |
|---|---|---|
| Tax carried to the third decimal, rounded up to the next cent when that digit is over four (R1) | Streamlined Sales and Use Tax Agreement, ยง324 Rounding Rule (as amended through December 20, 2024) | |
| Worked rounding examples, used as test vectors (R1) | Georgia Department of Revenue, Rule 560-12-1-.05, Rounding Rule for the Collection of Sales and Use Tax | |
| State rates, average and highest local rates, combined rates as of July 1, 2026 (R4) | Tax Foundation, State and Local Sales Tax Rates, Midyear 2026 (Sales Tax Clearinghouse and state revenue departments) | |
| State rates with three decimals: Minnesota 6.875%, Missouri 4.225%, New Jersey 6.625%, New Mexico 4.875% (R4) | Tax Foundation, State and Local Sales Tax Rates, 2026 (January edition) |
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