Sack the one who tells (7)

I believe the answer is:

cashier

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'sack' is the definition.
(I've seen this before)

I don't understand the rest of the clue.

(Other definitions for cashier that I've seen before include "Money handler; dismiss from the forces" , "one taking money" , "Remove from service" , "I search (anag) - dismiss from armed forces with disgrace" , "may be a shop-worker" .)

I've seen this clue in The Globe and Mail.

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