The post-1982 cents (almost all zinc) only have 0.6 cents worth of metal but they are a money loser when you factor in the manufacturing cost.
63% of all the circulating coins minted in 2010 were cents. Do you know how many government jobs would be eliminated if they stopped making cents?
That's why they haven't stopped making them.
As I offered, pennies are hoarded, which is why we need so many of them. It's not really intentional hoarding so much as casual, like my penny pig. And also because they're discarded by some, as has been demonstrated.
I'm very much in favor of reforming the currency to eliminate both pennies and dollar bills. No pennies, dollar coins only, because they're a lot more durable. I suspect that a coherent argument could be made for a $5 coin, as well.
CPA's point is overblown wrt fill ups on gas. The vast majority of such transactions are done at the pump, with credit cards, the transactional billing for which can still be done in cents. Only cash transactions need to be rounded.