The tax you should be paying. You are not paying.

What do your 2010 online holiday shopping purchases have to do with the budget gaps many states are struggling to fill right now? In the eyes of some state and federal legislators, the sales tax that is not being collected by many online merchants is revenue that could help stem the bleeding of state treasuries.

What most shoppers don't know is that they should be paying taxes on most online purchases, even when the retailer doesn't collect.

Because of two decades-old Supreme Court decisions, a state cannot require "remote sellers" -- any business without a physical presence in that state -- to collect and remit sales tax. Despite this, sales tax is still due in most states, and it's the purchaser's responsibility to pay it.