The goal of money is to be a common medium of exchange where it is understood that although the money is actually worthless, everyone will except it because everyone else will accept it. Pennies and nickels (although especially pennies) do not meet this task. Although the coins have a set value, the value of them is so low that there is nothing equal to them in value in either goods or services. They are hard to handle and deal with and do not perform the task of money.
Pennies cost 2.41 cents to make and nickels cost more than 11. This is money wasted on things that don't pay for anything let alone themselves.
Along with the cease of minting these coins, $1 bills should be stopped. They are commonly used for purchasing things and their make-up gives them too short a life.