Try an initial clear first. This will jump the machine out of any current task and return it to REG mode. Make sure you do the initial clear, not the RAM clear. The initial clear varies between models so look in your manual for the correct method for your machine. If you need a manual, c-tech collective have one here:
http://the-checkout-tech.com/manuals/cashregisters/Samsung_ER-5200M_and_ER-5240M_operating_programming_manual.html
Registerman
September 2010