Dell generally charges tax on all consumer purchases to all states.  In any case, you'd have to pay the tax to your state yourself, even if Dell did not collect it.

Just what makes you think it's fraud?  Dell collects the tax and remits it to your home state's revenue department - just as you must do if you buy that book from Amazon or that guitar online.  Just because a company does not collect tax in your state doesn't mean you don't owe the tax - you do, in fact, owe the tax (check your state's tax return form for the details - there will be a remit line in there).  For Dell to collect tax it MUST have an agreement to remit the collections with your state's revenue department - just as Best Buy does when you buy something in the store. 

Since Dell starting selling computers in Best Buy and other retail outlets they now collect sales tax in most states.

If I buy a Random House book at my local Barnes & Noble, I pay tax on it.  If I order the same book from Amazon, there's no tax.

If I buy a Fender guitar at the Guitar Center store, I pay tax.  If I order a Fender guitar online from MusiciansFriend etc.,  no tax.

Seems to me like Dell is collecting a tax that they are not entitled to.  I have filed a consumer fraud complaint with the Attorney General's Office in my state.