I mean, there are countries where tourists don’t have to pay tax on top of items (meaning they pay for it tax free given if they presented their passport upon purchase proving they’re merely only a visitor, that won’t work on expats though). Those countries usually have tax refunds when visitors are leaving (basically reclaiming VAT whilst at the airport).
Sales tax is a state deal not federal. Not all states have sales tax. Visit Oregon, for instance.
But I believe the idea is that the transaction, regardless of who, was in the state. And the state wants a cut. The state don’t care if you are taking the goods out of the state or not. The state wants its cut.
Not on everything. If an Oregonian goes to Washington and shows ID for non consumables it’s not taxed.