Tax

Figure somewhere between 6 - 8.25%

In San Diego sales tax is 7.75% but in Los Angeles I think it's 8.25% - I think NYC is just as high as Los Angeles. Other U.S. States have as low as 6%.

The sales tax should be calculated for the county/state that you live in.
 
I'm not so sure because my parents do all that stuff but you can ask the SA before you purchase something.
I'm guessing its something similar to the VAT process...filling a form, have your ticket with you and all that