Because the phrase ‘by the penny’ is implied that whatever it is, will squeeze all the value out down to the singular digit, because the penny has a value of 1 cent as we all know. However, with the penny no longer in production, how soon can we expect a time where nobody will say “by the penny”?
I like to imagine that inside the car door the window is stored in a roll. Of course that reverses the normal meaning of “roll up” since in this case the roll is at the bottom, unlike blinds or toilet paper.