A taxing drink

Today, I hit up Tapioca Express in Cupertino with Mom. During the car ride back, we were both vexed by the following:

Jasmine Milk Tea (delightful, if a bit sweet) cost us $3.30. But the menu listed it as $2.75. Now, tax in Santa Clara County is 8.25%. So how does a drink that's less than $3 ratchet up a tax of $0.55? We then spent a good two minutes doing this:

Cat: Wait, wasn't it $2.75? How did it end up being $3.30?
Mom: ...
Cat: Cuz even if you rounded the $2.75 to $3, and the 8.25% to 9%, the tax still shouldn't be more than $0.27. (For the math-impaired: 3 x 9 = 27.)
Mom: ...
Cat: (doubting her mental math skills)...Right?
Mom: (silent for 30 seconds)
Cat: (silent for an additional 30 seconds, feeling either cheated by Tapioca Express and/or ashamed of being a math-incompetent Asian)
Mom: (digs up receipt)
Cat: Oh. They charged us $0.30 for tapioca.

Mystery solved. Also, I don't know if I used "ratchet" correctly. I don't think I did. But more importantly, who charges extra for tapioca? At a boba store?! WITHOUT TELLING THE CUSTOMER?!