As someone from a culture where tipping is not standard, I found the first tip calculator section quite unclear. I didn't know whether taxAmount was the extra due to tax, or the total amount after tax. I also didn't know whether tipAmount was calculated from the original bill or price after tax.
I see a lot of 9 hours 9 persons 9 doors in the concept. The puzzles were just challenging enough, without taking the focus from the storyline. Generally impressive.
 "The Programmer RPG"){kind=icon}
 "no-one has to die."){kind=icon}
 "UpBot Goes Up"){kind=icon}
emmm, I see how this could be confusing. sorry. I taught for a semester in China, and we never tipped. Give me a shout if you're still stuck.