Capital gains tax cut, roughly zero (8)
I believe the answer is:
santiago
'capital' is the definition.
(capital of Chile)
'gains tax cut roughly zero' is the wordplay.
'cut' means to remove the last letter.
'roughly' indicates anagramming the letters.
'zero' becomes 'O' (O resembles 0).
'gains'+'tax'='gainstax'
'gainstax' with its last letter taken away is 'gainsta'.
'gainsta' with letters rearranged gives 'santiag'.
'santiag'+'o'='SANTIAGO'
(Other definitions for santiago that I've seen before include "City" , "Chilean capital" , "Capital of Chile" , "Chile's capital" , "South American capital" .)