If I order a playstation 3 for $299.99 that exactly how much I would have to pay at Amazon. Stores like GameStop tack on an extra $30 sales tax.
You only pay sales taxes on purchases made from stores that operate in your state. Unless, Amazon (or the seller that is selling through Amazon) has a physical location in your state then you will not be charged any sales tax. This is one of the many reasons I choose Amazon..... also the free super saver shipping!
Online businesses are considered as old-style catalogue businesses. They can ship state-to-state and not collect sales tax.
These types of businesses are only required to collect sales tax where they have a business presence in a state that requires them to collect sales tax in that state.
Currently Amazon is only required to collect sales tax to items sent to Kansas, Kentucky, New York, North Dakota, and Washington State.
By the way, in most states with sales tax when you buy something from Amazon and don't pay tax, you are supposed to fill out a form and send the tax in to your state yourself. Some states have even added this form to their income tax return. Yes, I realize that the number of people who do this is very very very small.
The only time you must be charged State Sales tax is if the seller has a store in your state. If you order from Target, Sears, JCPenney, etc. you will be charged Sales tax since they have stores in all states. The seller only charges sales tax to people who are in the same state as the seller.
If you order it & go through the checkout, once your address is added it will then determine your states sales tax & charge you that rate.
They get the money from the person who is selling it, so they don't have a need to put on the extra sales tax