Charges pound to block opening up (5)
I believe the answer is:
tolls
'charges' is the definition.
(toll is a kind of charge)
'pound to block opening up' is the wordplay.
'pound' becomes 'l'.
'to block' is an insertion indicator (block can mean to fill a hole in something).
'opening' becomes 'slot' (slot is a kind of opening).
'up' is a reversal indicator (in down clue: letters go upwards).
'l' placed into 'slot' is 'sllot'.
'sllot' back-to-front is 'TOLLS'.
(Other definitions for tolls that I've seen before include "bars" , "Chimes mournfully" , "Hemingway novel 'For Whom the Bell . . . . .'" , "Road charges" .)