Actually there are many 'delayed' rebates back to the dealers that don't happen until months after the vehicle has been sold (volume kickbacks, incentives for selling certain models/configurations etc. etc.). On any given car I doubt they know the true actual cost until the end of the MY.
Then there is all the added profit from the tag, prep & title fees they charge that cost the dealer very little & are mostly pure profit + plus any mandatory add-ons (paint protection, window etching, nitro tire fill etc.) + any ADM they tag you for.
You can be certain they are making huge $$ even selling the car at (what they call 'invoice') - 2 or 3% !!!