The cost of minting pennies far exceeds their face value. The direct cost to the US taxpayer is in excess of $100M annually as it costs 2 cents in raw material and processing to create each 1 cent coin.
Very few vending machines accept pennies.
The time involved in processing cash transactions and making change involving pennies is a substantial drain on the economy. It has been estimated that the average American wastes 2.4 hours per year handling pennies.