Amazon, the online merchandise juggernaut, will collect sales taxes from all states with a sales tax starting April 1. Tax-free shopping will be over as of next month in Hawaii, Idaho, Maine and New Mexico, the four remaining holdouts. Since the beginning of this year, Amazon has added a number of states to its roster of jurisdictions where it collects sales taxes.

Amazon shipping center in Schertz, Texas Robert Daemmrich Photography | Corbis | Getty Images

"Maine businesses can go toe-to-toe with the very best out -of-state companies, provided they are competing on an equal playing field," said George Gervais, commissioner of the Maine Department of Economic and Community Development, in a statement. "Amazon's decision to collect and remit sales tax to the state of Maine is an important first step in leveling the playing field," he said, noting that the increased revenue from sales levies will help lower the state's income taxes. After April, the only states in which Amazon won't collect taxes are Alaska, Delaware, Oregon, Montana and New Hampshire. These five states don't have sales levies.

Missing windfalls

The National Conference of State Legislatures estimates that states lost out on $23.3 billion in revenue in 2012 due to their inability to collect sales taxes from online purchases. How states treat sales taxes for web and catalog purchases is tied to a 1992 Supreme Court case, Quill Corp. v. North Dakota.

The court ruled that states couldn't require retailers to collect sales taxes unless they had a physical presence in the same place where the buyer is located. Major online retailers — namely, Amazon — more and more fall under that rule by building data centers, warehouses and other facilities in multiple locations.

You still owe

Even if your online retailer doesn't assess a sales tax because it doesn't have a brick-and-mortar location in your home state, your state may require you to pay use taxes on your purchase, according to Richard C. Auxier, a research associate at the Tax Policy Center. Use taxes, which apply to items you buy outside your state of residence, generally are assessed at the same rate as a sales tax. The burden of reporting use taxes falls to the consumer, Auxier said. "Everyone owes taxes on online purchases, be it from Amazon or a small retailer," he said. "The question we deal with is 'Who collects the tax?'"

Reporting responsibilities

States that assess use taxes give their residents a way to report it. California, for instance, provides a worksheet for taxpayers to calculate what they owe. New York, meanwhile, offers forms for reporting these levies when you file your income tax return. In the Empire State, you may be subject to penalties and interest on any back use taxes. In reality, states haven't been particularly stringent about collecting these use taxes — and many shoppers don't even know they owe.