Conversation so far:
what does it mean when your drawer is over
An overage is when your drawer is over the amount your POS report says you should have.
what does it mean when your cash drawer is under
A shortage is when your cash register's total is short.
why would a cash register be short
Cash register shortages could mean cash was either lost, stolen, or counted incorrectly.

Question: who is responsible
Self-contained rewrite: who is responsible for cash register shortages