If you are a student at Caltech I am assuming that you are a foreign student. My brother has a Phd in mathematics and teaches computer science. Most of his students are foreign since the vast majority of Americans are mathematically illiterate.
In America when you purchase from a company in another state and that company does not have nexus ( offices, stores etc.) in your state they are not required to charge sales or use tax. You are suppose to report the use tax on your state income tax form however it is impossible to track and only a fool would report and pay the tax. How many people report sales tax for products that they purchase from Amazon?
Personally, I would never purchase merchandise directly from Apple due to the fact that they charge and collect sales tax. There are many well respected Apple retailers online that discount Apple products, offer rebates and in many cases give away free printers, software etc. with your purchase + they do not charge sales tax. Check out Amazon, Macconection, MacMall, B&H Photo, J&R, Powermax and Sweetwater. Depending on the model you could easily save $400 or so through discounts and avoidance of sales tax.
If I am correct and you are a foreign student at Caltech, welcome to America!