Disbursement of cash

I want to set a button that I can take cash out of the till. For example if I buy milk for staff they can press a button add the mount and the till drawer opens so a receipt can be put in. I also would like it to deduct from the takings of the day so if we took £10.00 and milk cost .50p the takings would show as £9.50 with a disbursement of 50p

If you can help or know of a way please let me know.