To further eliminate the possibilities of confusion, at least in Washington state, there is a state-wide retail sales tax, and there are additional sales taxes based upon the city or county where the transaction occurs. There are over 400 different taxing regions in Washington state.
Even if you mean sales tax, that's set on a state-by-state basis, and you only have to collect sales tax in a state if you have a physical presence there:
In the US it seems the onus is put on the consumer rather than the business. We should all be declaring our out of state purchases on our tax returns... http://en.wikipedia.org/wiki/Use_tax
More information:
https://www.sba.gov/content/collecting-sales-tax-over-intern...