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
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:
https://www.sba.gov/content/collecting-sales-tax-over-intern...