Work out what a price comes to with sales tax, or go the other way and pull the tax back out of a total you have already paid. Pick Add tax if you know the shelf price, or Remove tax if you only have the receipt total. Type your local rate, or tap one of the preset rates to start from a typical figure. The result shows the price before tax, the tax amount and the total, so you can check a receipt line by line.
How it works: Adding tax is price × (1 + rate ÷ 100); the tax itself is price × rate ÷ 100. Removing tax works backwards from the total: pre-tax price = total ÷ (1 + rate ÷ 100), and the rest is tax. Figures are rounded to the cent, so a long receipt can differ by a cent or two from the store’s total, which taxes each line separately.