Pennies are so useless as legal tender that there's genuine debate about whether we should even keep them around. It wastes energy and resources to produce them, they're disproportionately costly to make (1.7 cents per one-cent coin!), and there's not a vending machine on Earth that will take them. A lot of people reportedly just throw them away. But they're still minting the little suckers, for now, so you might as well make them justify their expensive existence. Which means you could dump them in the Coinstar machine ... or you could use them to make an awesome, cost-effective copper flooring that is, excuse me, really money.