To perform the following cheat you will need a bookshelf and there is the possibility that you may lose the books you have purchased from the book store.
Step 1: Buy the cheapest bookshelf there is (if you don't already have one).
Step 2: Click on the bookshelf and select 'Browse'.
Step 3: Sell one of the books then go to 'Buy' mode.
Step 4: Click on your bookshelf and sell it and then click the 'Redo' button and go back into 'Sim' mode (this will double the amount of books in your bookshelf).
Step 5: Repeat steps 3 and 4 until you have 100 or even 1,000 of each book type in your bookshelf.
Step 6: Click 'Browse' and sell all of those books.