If you don't - like in the case where you have a car shipped to you from out of state - then you pay the sales tax in your home state when you go to register your car. Similar in the case where you buy a car in a state with no sales tax and register it in a state that does charge sales tax. For instance, Oregon to Utah. You would pay no tax in Oregon but when you register the car in Utah you will have to pay Utah sales tax rates. If Utah rates are higher than the sales tax you pay in another state, you will have to pay the difference. If the sales tax you pay out of state is higher than where you register the car, then you are just out of luck.