Do ninety-nine of them have a cheapening appearance? (5)
I believe the answer is:
pence
I'm afraid I can't even guess how this answer relates to the clue.
Can you help me to learn more?
(Other definitions for pence that I've seen before include "Small coins" , "Small coppers" , "little money" , "Little coins" , "Old money for the US vice-president" .)