Should you keep a library book till you finish reading when you know some’s waiting for it?

I borrowed Juliet Naked, the latest Nick Hornby novel, from my local library a few weeks ago. It is due today.

I borrowed Juliet Naked, the latest Nick Hornby novel, from my local library a few weeks ago. It is due today. Unfortunately, I’m only about halfway through and can’t renew it, because it is on hold for another patron. I’m willing to pay the penalty, 25 cents a day, so I can keep reading. May I do that, or must I return it knowing that someone else is waiting for it?