Yeah, that's nice in theory, but most states require you to pay the tax anyway, even if the retailer doesn't collect it. For example, Massachusetts has a 6.25% sales tax and New Hampshire has no sales tax. If I drive up to NH and buy something, MA still expects me to pay tax on it if I'm planning to use the item primarily in MA. There is a section of the income tax forms dedicated to calculating how much sales tax you owe on out-of-state or online purchases where the retailer did not already collect it. Just because most people fail to do this doesn't mean you're not supposed to.
What I find most interesting about this Target thing is that they are charging $499.99 for it when Apple and Amazon only charge $499. Wonder why they felt like tacking on that extra 99 cents?