Today the S. Ct. decided a case called South Dakota v. Wayfair, et al. It will be on the news. South Dakota had a law requiring out of state sellers who sell stuff and ship it to S. Dakota to collect from S. Dakota resident purchasers the appropriate S. Dakota sales tax and to remit the tax to the state. Prior S. Ct. cases had said that a state could not do this, and today, the S. Ct. in a 5-4 decision reversed the earlier cases and said the S. Dakota law was permissible. Therefore, a state can require an out of state seller to collect the applicable sales tax.
Let's say you live in S. Dakota, which has a sales tax and you order some California cabernet sent to you from the winery. The winery may be compelled to collect the S. Dakota tax from the consumer and remit the tax to S. Dakota.
So, let's say you buy stuff from Amazon. You might well not be paying sales taxes on those purchases today. You might well be paying sales tax on them shortly.