1. The Supreme Court has heard a case where the states have imposed sales taxes on outside vendors whose products go to the state's residents. Previously, vendors who had a business location in the state were required to collect sales tax for sales to the same state's customers. Now states want all vendors to collect the sales tax.

2. Congress periodically hears proposals to impose a national sales tax, which has momentum with lawmakers who consider it unfair that states generally aren't collecting a sales tax. As in Canada, though, there's no reason the federal government and the state (province) couldn't be blocked from each imposing taxes - assuming the states win the Supreme Court argument.

In addition, there are use taxes. If you buy a product and don't pay sales tax, some states expect you to pay a use tax for bringing it into the state. It adds up for major purchases.

My daughter lives in Cook County, Illinois. She bought a car in a different county and last week received a tax bill from Cook County for a 1% use tax - and that involves two counties in the same state!