A couple points, if I may.
If a business doesn't charge you sales tax, and should have, they are on the hook. So it is safer for them to charge you, and you figure it out in your state.
The good old days of "I bought it off the Internet, so I don't have to pay sales tax" were never there. If you bought something off the Internet, and you didn't pay sales tax to the seller, you were supposed to pay tax to your state, by self reporting. We all know that didn't happen, but technically, and legally, we were all supposed to be doing that.