TULSA, Oklahoma - Cyber Monday shoppers are expected to spend a few billion dollars according to financial experts.

While you're looking for those deals online, keep track of your receipts because it could cost you if you don’t.

A new law requiring Oklahomans to report online purchase for sales tax has been in effect for nearly a month. Companies that operate in the state automatically apply the sales tax, but you’ll need to keep track of the companies that don't.

The deals are at your fingertips, as websites offer big "Cyber Monday" sales; but when you're making your purchases, pay attention to what you're paying at check out.

Eillen Robinson with Gardner's tax service said you should also keep your receipts.

"There are places where you can purchase something online that may not charge sales tax, and in that case you are required to report to your tax preparer what you purchased online that did not have sales tax charged," she said.

The new law, implemented November 1st, gave out of state retailers the option to charge sales tax for Oklahomans up front or send them a notice of how much they owe. But, ultimately, it's up to the customer to keep track.

Right now, only four percent of Oklahomans pay online sales tax, but the state is cracking down.

Robinson said, "You're gonna have people who say, ‘I haven't been doing this, I mean, what do I do? Do I need to file back stuff?’ Just start doing it now."

According to the state auditor, sales tax makes up $2 billion of the state's budget, however, $300 million a year is lost due to unpaid online sales tax.

"Unless you're spending thousands upon thousands of dollars, you aren't going to be paying quite a bit of money,” Robinson said. “It's just that little bit that adds up - a dollar here, a dollar there."

Robinson adds, if everybody pays their fair share, it'll not only help the state but cities and counties too.

"All of that factors in to make sure that Oklahoma thrives," she said.

Robinson said you should keep your online receipts with the rest of your tax documents, and, if you can't remember what you've bought, many companies will let you go back and look at old records.