From The Collaborative International Dictionary of English v.0.48 :
Cash register \Cash register\
A device for recording the amount of cash received, usually
having an automatic adding machine and a money drawer and
exhibiting the amount of the sale.
[Webster 1913 Suppl.]
From WordNet (r) 3.0 (2006) :
cash register
n 1: a cashbox with an adding machine to register transactions;
used in shops to add up the bill [syn: cash register,
register]