Work with a known applicable percentage in the manual sales tax calculator. These guides explain arithmetic, not address-based rate lookup or transaction eligibility.
US · EN · sales-tax
Multiply the taxable amount by the applicable percentage divided by 100, then add the tax to that amount. Establish the taxable base and rate first: a calculator performs the arithmetic, not the legal classification.
US · EN · reverse-tax
To find a price before sales tax, divide the tax-inclusive amount by one plus the percentage divided by 100. Use a known rate and a total containing only the base and that tax; a receipt alone may not supply enough information.