Noughts for example used in rough estimates? (5,7)

'in rough estimates?' is the definition.
I know nothing about this answer so I cannot tell whether this works.

'noughts for example' is the wordplay.
I cannot quite see how this works, but
'noughts for example' could be 'numbers' (nought is a kind of number) and 'numbers' is found in the answer.
The remaining letters 'round' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...

'used' acts as a link.

Can you help me to learn more?