Why can't the penny be discontinued?

The Cent, along with any other denomination can be discontinued if Congress feels like it. However, most of the denominations that the US has made have not been discontinued, with only the half cent, two cent, three cent (silver and nickel) and the 20 cent piece being discontinued for various reasons. The big reasons why the cent is unlikely to be discontinued is because people don't like paying more for things and the zinc lobby is quite powerful (pennies are mostly zinc today).