Share out a tax return (5)
I believe the answer is:
allot
'share out' is the definition.
(allotting is a kind of sharing out)
'a tax return' is the wordplay.
'tax' becomes 'toll' (I've seen this in another clue).
'return' is a reversal indicator.
'toll' written backwards gives 'llot'.
'a'+'llot'='ALLOT'
(Other definitions for allot that I've seen before include "Earmark" , "Dedicate" , "Assign (to someone)" , "Assign or distribute" , "Ration" .)