[greenyoda]

According to Nolo.com[1]:

"If an online retailer has a physical presence in a particular state, such as a store, business office, or warehouse, it must collect sales tax from customers in that state. If a business does not have a physical presence in a state, it is not required to collect sales tax for sales into that state. This rule is derived from a 1992 Supreme Court decision which held that mail-order merchants did not need to collect sales taxes for sales into states where they did not have a physical presence."

Since your business, being located outside the U.S., presumably has no physical presence in any U.S. state, it doesn't seem like you need to collect sales tax.

[1] http://www.nolo.com/legal-encyclopedia/sales-tax-internet-29...