I am currently in college majoring in business administration. When I grow up I plan on opening up my own computer retail store.

To save money I am trying to figure out how to program my own Web (Point of Sale)POS System that could run on the registers. Much similar to one that MerchantOS.com offers as a service. I want to make it part of the web so I can access my inventory and make orders any where I am. Does anyone know of a good program code that will be best to do for this where I can be very safe?

I currently know a little bit of PHP and Javascript, also I know a lot about HTML. I know that it would take a while to do, but I am ready to a big project.