Most recent cash registers have a keyboard membrane - a laminated plastic sheet with electrical traces on it - that contains the contacts/switches for the keys on the keyboard. Liquid spills get between the laminated sheets and interfere with the functioning of the switch contacts.
If you feel bold enough to open the case of your register - observing all safety and ESD precautions, of course - you may be able to disassemble the keyboard, remove the membrane and dry it out using GENTLE heat (a blow dryer on the lowest setting, place it in a warm sunny spot for a while, etc.). BE CAREFUL - too hot and the membrane will melt / warp and then it wil be REALLY useless. This is not a job for the faint-of-heart; you should have some previous experience repairing electronic device to attempt this.
Failing this, you should be able to take the register to a dealer in your area and have the membrane replaced.
Good luck ...
Steve, September 2009
