I am making a cake for my husband's graduation. It's supposed to be three tiers and I want them to look like spines of books (sort of as if it was a round bookcase) The cakes are already filled and crumb coated, but I'm unsure about how to best use the fondant to create the book spines and the tops of the books where the smaller tier doesn't cover. Has anyone done anything like this or have any ideas?

Wow, that's a tall order
To make book spines, cut rectangles of fondant & dry on flower formers to get the rounded shape.
Cover the tops of the cakes w/b'cream or fondant - your choice just as if it was a table or shelf.