Pennies do not have enough buying power today due to inflation and the rising value of raw copper. They are not worth manufacturing because it costs 1.8 cents to produce each one. Therefore, the penny is dead weight to the US economy.
Stop producing pennies, but allow the penny to remain legal tender. Send any pennies collected to the US Mint to be melted, thus steadily decreasing the supply of pennies. Prices will still have single cents, so when you pay by card, the exact amount will be deducted from your account. But the difference is that if you pay by cash, the price will be rounded to the nearest five cents (The difference in rounding will not make a difference). Retiring the penny will not single-handedly balance the budget, but it is the simplest and most rational step to take.