It is totally dependant on each game.
I would say there are two measures of sales, one is the specific titles expectations (from the public, us or journalists/analysts) the other is how profitable it becomes due to good sales.
For instance if GTAIV on both platforms failed to make 12 million sales it wouldn't be considered good sales at all when previous versions have all sold so many more copies (double it with San Andreas)
But profit wise Take2 may have broken even already, assuming $10-20 per copy goes back to Take 2 they needed to sell roughly 6 million (@$20) or 12 million (@$10)
That is assuming the $100 million development figure is correct, and adding $20 million for advertising etc.
That of course doesn't factor in Microsofts money either, but as I am not sure on the specifics of that I ignored it, I have heard it was a loan to Rockstar that is to be repayed, or perhaps it was purely money to Rockstar and might not have made it to Take 2s hands (although I think R* is owned by T2 so I doubt this)
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That is an example of a massively high budget game though, for which profitability needs incredible sales, MGS4 for instance I am not sure will ever make Konami a profit because it will surely need 5 million sales if not 6 or 7 just to break even.
