There's an actual thing that says that pennies are only legal tender up to $20, I think?Yeah, and businesses don't have to accept your payment if you try to do so in all pennies, either.
<searches around on the Internet>
Ah. Prior to the Coinage Act of 1965, coinage was not considered legal tender if it exceeded $10, and pennies were technically only valid in aggregates up to 25 cents.
--Patrick