With the new $10 bills set to debut next year, you might be thinking that those old bills are worth holding onto. You wouldn't be alone, but you may have to wait a while.

Whether it's the old-style ten-spot many of us grew up with (which was around in similar form from 1929-99) or the new-style bill with the larger image of Alexander Hamilton (which debuted in 2000), people will hold onto their old bills like -- well, like they're going out of style.

"Whenever they made the announcement that they're going to change the bills, a lot of people start to pull them out of circulation," said Emmett Yonce, owner of Yonce's Coins in Roanoke.

"They're collector-investors," he said. "They try to pull the better-condition bills out... and hope to sell them."

While stashing some bills under the mattress before they disappear might seem like an investment, chances are you're better off putting it in the bank and earning the interest.

Because, while a $10 Gold Certificate from 1922 sold for more than $350 on eBay Wednesday, a 1934 $10 bill was going for $9.99.

-- Andrew Kantor