[ChuckMcM]

The US is, by definition, a tax nightmare because there are generally three (and sometimes four) tax jurisdictions to consider;

   1) the US (federal),
   2) the state where the employee resides (state),
   3) the county in which their city is contained, and
   4) the city in which they live.

The other thing is that "sales tax" is collected by states, not by the Federal government. They are generally pretty inept at collecting tax from out of state entities and won't bother you until you are doing a lot of business in their state. Nominally your customers are responsible for paying it, not you.

Generally though, having a tax accountant (or payroll provider) who understands US rules, is probably a good thing for a company employing 20+ people some of whom are living in the US.

[sfrailsdev]

Actually where an employee lives and where they work may both be relevant, if different.

[Spooky23]

Be careful with the assumption that states are inept! Some are very capable, much more so than the IRS.