I'd love to take the penny out and convert our coinage to larger coins. There's only one problem: the mathematics of it.
If you remove the penny, then all the remaining coins become awkward multiples of five -- five-cent nickels, ten-cent dimes, twenty-five-cent quarters, and the occasional fifty-cent half-dollar. Every cash register in the country would have to be reprogrammed to round prices to the nearest multiple of five. You could also just chop off the last digit and convert everything to multiples of ten, but the same problem exists. The most practical option would be to convert everything to whole dollars, but too many goods still cost less than a whole dollar to make that possible.
The penny is necessary because American money is calculated to the nearest one-hundredth of a dollar, and therefore we need some coin to represent that exact value.
If you've got too many pennies in jars, do what I do: keep them in your pocket and spend them in stores to get exact nickels and dimes back. Or drop them in the tip jar at your favorite coffeeshop. Or keep them in your car -- automated toll booths, at least the ones in Illinois, accept pennies just like any other currency. It's valueable money, after all, not just circular dirt.