A dimwitted bookstore clerk at the world-famous Juilliard School is singing the blues in jail after he was busted for allegedly swiping $10,000 in a scheme cops called classically dumb.

Pete Rosado, 28, of Manhattan, rang up $10,000 in legitimate sales of books, CDs and other items at the Juilliard Bookstore at 144 W. 66th St. — and then used copies of the receipts to void the purchases and pocket bogus cash refunds.

Rosado was charged Monday. He’s not a student at Juilliard, whose grads include musicians Wynton Marsalis and Yo-Yo Ma and actors Kevin Spacey and Bebe Neuwirth.