Pair of coppers employed for a trivial sum (8)
I believe the answer is:
twopence
'a trivial sum' is the definition.
(trivial sum of money)
'pair of coppers' is the wordplay.
'pair of' becomes 'two'.
'coppers' becomes 'pence' (I've seen this before).
'two'+'pence'='TWOPENCE'
'employed for' is the link.
(Other definitions for twopence that I've seen before include "Penny plain, - coloured" , "Fiftieth of a pound" , "Not much money" , "bit of history" , "Low-value coin" .)