Hi Jenney,
I haven't worked with the 500dx so I don't have notes for it. If you look through the manual to find department programming, there should be a price setting. If you don't have the manual, one of the users has a 500dx manual here:
https://the-checkout-tech.com/manuals/cashregisters/Royal_500dx_instruction_and_programming_manual.html
Hope this helps
Registerman
February 2015