Mrs Abster is quite right that most financial matters must be discussed in public. Although the question is perhaps a bit vague.
It is, for example, acceptable to exclude the public from a discussion where commercial confidentiality is required or where the council's negotiating position would be compromised.
My golden rule is that the public should be excluded as rarely as possible, and for as few items as possible. But where confidentiality is essential, then exclusion has to be voted for and applied. This should be done even if no members of the public are present, since otherwise someone arriving at the meeting during the item could not be excluded.