You are supposed to voluntarily remit that tax to the state.
I'm aware that such a law exists. But saying it is "widely ignored" has to be the understatement of the year. People buy stuff from Amazon in vast numbers and very, very few people then "voluntarily" pay sales tax on it at the end of the year. Which is why the states have been trying to change the law so that places like Amazon will collect the tax right at the time of purchase.