I say keep the penny. It's an American tradition, just like Thanksgiving. We don't need Thanksgiving but we keep it because it's a tradition.
Merchants like to price their goods at .99, 1.99 2.99, 3.99 etc. and they wouldn't be able to do that anymore.
If you get rid of pennies, nickels would become the new pennies and we would soon be complaining about the uselessness of nickels. People would say that we should round everything off to the nearest dime. Then the nearest quarter and so forth.
Here's an idea for those who don't like pennies: Don't use them. If the store clerk asks you for $3.66, you pay $3.70 and say, "keep the change". Or hand over $4 and ask for 30 cents change.