If they win a single penny, you betcha that they get to keep the money. If they winR$10,000 or more, they may take some out to cover the taxes. But you get the remainder, such asR$8,000 for aR$10,000 win. They always get to keep their winnings, whether it is a penny or a million dollars.
As far as anyone publicly knows, the Deal or No Deal Banker is not tipped off to any secret information. They are not told how much is in each case and are not keyed into anything that would be considered game-changing information.