National Cash Register Keys Reproduction. 1 key operates the lock on the lid. 2 key operates the lock on the left side of the cash register, it locks the keys so they cannot be pressed down. 3 Bell key leftside, allows the bell to ring or remain silent when the cash register is used. Reset key resets the total adder back to zero, located under the lid. Free shipping to the lower 48 States. E-mail any questions.