Money was hard to come by during the Depression era days in which To Kill a Mockingbird is set, and for children it was a true rarity. Jem and Scout have little money to spend; after all, "there was nothing to buy and no money to buy it with." Scout is excited when Jem takes his birthday money to Elmore's department store to "buy a miniature steam engine for himself and a twirling baton for me... I thought it generous of Jem to buy it for me." The baton cost all of 17 cents. So, when Jem got the chance for a small payday from Atticus, he jumped at the chance. Scout knew something was up when Jem, and not Atticus, walked her to school on her first day.
I think some money changed hands in this transaction, for... I heard an unfamiliar jingle in Jem's pockets. (Scout, Chapter 1)