Question

How do I calculate sell tax

Answer 1

Well, it depends on the state you live in.

In Tennessee, it is pert-near 10% (thanks govt)
So lets say I bought an item with a price of $10.00

I would multiply $10.00 by .10 (just move the decimal of the percent over two places to the left)
So the Item would cost $1 extra, =$11.

Answer 2

If sales tax was 8%, make the decimal form look like .08