It depends on the restaurant. I've seen some that charge per bottle, some that don't charge for the first but charge for any others, some that never charge, and others that only charge one fee for however many you want to enjoy.

There's no right answer, it's strictly what the policy of the restaurant is.

I have a friend who opened a place, and the two decisions he worried the most over, asked future customers, checked everybody around him, were which four beers on tap he would carry (only four taps) and the corkage fees.

He decided not to charge at all.