Work at cash register (4)
I believe the answer is:
till
I believe this is a double definition.
'work' is the first definition.
(to till is to work the land)
'cash register' is the second definition.
(I know that cash register can be written as till)
'at' acts as a link.
(Other definitions for till that I've seen before include "Cultivate - cash drawer" , "Drawer holding money in shop." , "Up to (a point in time)" , "Cash found here" , "Plough" .)