Responsibility for tax (4)
I believe the answer is:
duty
This clue is a double definition.
'responsibility' is the first definition.
('duty' can be a synonym of 'responsibility')
'tax' is the second definition.
(duty is a kind of tax)
'for' acts as a link.
(Other definitions for duty that I've seen before include "Allegiance" , "Service - tax - office" , "Kind of obligation or tax" , "charge" , "A tax; compulsory task" .)