I usually wait until I leave the store to examine my coins because if I was in the cashier's position and didn't know how coin collectors think I'd think "wow, this jack butt thinks I shorted them change"
Anytime i get change I check for wheat pennies , nickels before 1960 ( I save them if not beat up), pre 1965 dimes and quarters, and i check the serial numbers of the bills for any oddities.