Total Check Out APP?

is there a app that scans all of the items that you are about to check out with at any store that will total up all of the items that is in your cart so that by the time that you get to the cashiers. you already know what the full price will be? if not can someone please MAKE ONE. that would be awesome i think. and if there is one already please fill me in and let me know what it is called. it would be very handy to have as a app for my phone. just cause i can do basic math doesn't mean that i necessary want to. yea im kind a lazy but i just thought since the saying is that there is a app for everything why not that too.