Using a calculator, enter the total, then subtract whatever percentage your local State Sales Tax is, in California, the Tax is 7.5%. If the total is $56.10, enter 56.10 into the calculator, then subtract 7.5%, giving you a result of $42.075. The bill, before tax, was $42.08.. . To find out how much tax you paid, enter the total $56.10 then multiply by 7.5% for a total State Sales Tax paid of $4.2075.