Ignoring the price discount on the mangos, the answer here is sales tax, right? Because otherwise it would be $15.70. It's a bad design that tax amounts don't show up on the itemized screen (but probably on the final screen after that).
Tell me if anyone knows for sure, otherwise I'm going to assume that's the issue...
EDIT: Thank you folks, asked and answered! Then, I'm back to being very confused...