How does POS retail tills work, cash registers with touch screens how do they work?
They are also known an point of sale and kiosks like the ones in mcdonalds or leisure centres

Very simple... the cash registers are like a computer. Places like mcdonalds the store manager can program each button to whatever they want it to be. Which pulls up the sandwitch and the price. At the end the total totals it up. For bigger retail stores like futureshop or any big corprate company they have tons of people working on the programming, same idea with the mcdonalds tills, except its more complex because they receive more products and prices change, they get the programming end all done during the day/week depends on price changes and new products, and in the retail stores at the end of each night they run POS. which updates all the buttons on the screen...

You also have a back office computer, and that organizes all the information that comes from the POS terminals, as well as the kitchen monitors (if fast food type system). Depending on whether your company that you work for is a chain, the store managers and general managers don't really have to change buttons, that is what corporate is for. They program all the buttons, and the prices and such. When you do your deposits, you use the POS terminal to count down the drawers. You also enter the deposits in the back office computer. POS systems are almost limitless as to what you can do with these. They are highly adaptable.