GNP's fine! Rolling in cash ... once (8)

I believe the answer is:

pfennigs

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'cash once' is the definition.
'pfennigs' can be an answer for 'cash'. I'm unsure of the 'once' bit.

'gnp's fine rolling' is the wordplay.
'rolling' indicates an anagram.
'gnps'+'fine'='gnpsfine'
'gnpsfine' with letters rearranged gives 'PFENNIGS'.

'in' is the link.

Can you help me to learn more?

(Another definition for pfennigs that I've seen is " Marks were made by such".)

I've seen this clue in The Everyman puzzle in The Observer.

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