Up to work checkout (4)
I believe the answer is:
till
I believe this clue is a triple definition!
'up to' is the first definition.
(thesaurus)
'work' is the second definition.
(tilling is a kind of working)
'checkout' is the third definition.
(a supermarket checkout)
(Other definitions for till that I've seen before include "cash container" , "Up to (a point in time)" , "Cashbox" , "Farm - money drawer" , "Cultivate - cash register" .)