Pennies from heaven.
I have realized what the simplest solution to the penny problem is. Since pennies cost more to make than they're worth, I had thought we should just divide our currency by five, and make a penny worth five cents, and so on. A much simpler solution would be to just drop the penny, and stop making the one dollar bill, replacing it with the dollar coin. Every time inflation erodes the value of the lowest denomination coin (except nickels are already more expensive than their face value), you make the lowest denomination bill into a new coin, and stop making the lowest denomination coin.