Extra tax daily covered by sharp increase (9)
I believe the answer is:
surcharge
'extra tax' is the definition.
'daily covered by sharp increase' is the wordplay.
'daily' becomes 'char' (I've seen this before).
'covered by' indicates putting letters inside.
'sharp increase' becomes 'surge'.
'char' inserted into 'surge' is 'SURCHARGE'.
(Other definitions for surcharge that I've seen before include "Extra payment" , "Excess fee" , "Additional cost" , "addition to bill" , "extra amount" .)