Your state has no sales tax. You pay no sales tax.
Your state has sales tax, you buy web/mail order from company that has a store in your state, you pay sales tax, even if it is shipped from another state.
Your state has sales tax, you buy web/mail order from a company that does NOT have a store in your state, you do not pay sales tax.
If you live in a shack in a few acres in Montana you have declared independent territory and are guarding with shotguns, you do not pay any tax, but you don't receive many imported goods either.
Your state has sales tax, you buy web/mail order from company that has a store in your state, you pay sales tax, even if it is shipped from another state.
Your state has sales tax, you buy web/mail order from a company that does NOT have a store in your state, you do not pay sales tax.
If you live in a shack in a few acres in Montana you have declared independent territory and are guarding with shotguns, you do not pay any tax, but you don't receive many imported goods either.