There is no mention of Scrooge taking a coin (or a farthing as Dickens would probably refer to it) from his nephew Fred.
Scrooge only meets the happy-go-lucky Fred a few times in the story. He meets him for the first time at the beginning of the story when Fred visits him at his office to wish him a merry Christmas. The second time is when the Ghost of Christmas Present takes him to Fred's Christmas party and he overhears what Fred thinks of him and his attitude towards Christmas.
The third time is at the end of the book; a transformed Scrooge visits Fred on Christmas day and then stays for dinner. They do, particularly during their first meeting, talk about money. Scrooge cannot understand why money means so little to his nephew and Fred cannot understand why Scrooge is so mean with his fortune—but no money changes hands.
You maybe referring to the end of the book, after Scrooge's transformation, when he donates a large sum of money to a charity and gives his clerk, Bob Cratchit, a raise.