Sales taxes on places like Amazon are set by your local taxing authority. There are whole business that calculate that for them based on your shipping zip code. Interesting problem, though: Zip codes cross tax boundaries. I live outside a small incorporated city with one of the highest sales tax rates in California. I'm in unincorporated County but my zip code reflects that city, so everybody charges me the higher tax rate. I actually bothered to ask the state for a refund on the two cars I bought recently and they sent me a rather large check.
I used to shop Fry's because there was one just a few miles away, and it was near some pretty great eateries. And if I needed a few small electronic parts I could get them on the spot. Lately though I'm finding much better deals on Amazon, EBay, and Digikey Electronics. The last hard drive I bought was 750 MBytes for just $28 on Amazon.
I'm picking up a terabyte solid state drive for "Little Beast" to make it a little bit faster.
Big Beast (Beast III) has one and so did Beast II.