I watched this movie when I was about 12 (20+) years ago. I think the film was set in the 50’s give or take. A little girl was sexually abused (unknowingly) by a man she knew, he gave her a small amount of change to touch him inappropriately. She eventually felt uncomfortable doing this, in which he forced her to do it eventually. I think this was in a southern setting in the 50’s.
Your description reminds me of “Bastard Out Of Carolina” starring Jena Malone. There is a scene where a girl’s step-father forces her to participate in touching him in the front seat of a car. He abuses her terribly in other ways, as well.
http://www.imdb.com/title/tt0115633/?ref_=fn_tt_tt_1