Charges that are round sums of course (5,4)

I believe the answer is:

green fees

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'charges that are' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.

'sums of course' is the wordplay.
'sums of' becomes 'greenfee' (I can't justify this - if you can you should believe this answer much more).
'course' becomes 's'.
'greenfee'+'s'='GREEN FEES'

'round' is the link.

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

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