So US indicated prices are net of tax. At what point in the transaction is the tax actually charged? At the point of checkout does the website lookup the tax rate for your location?
You got one answer, and it wasn't incorrect -- but it was incomplete.
Sales taxes in the US are astonishing, mind-bogglingly complex, and that's even without considering online purchases.
Some states have no sales taxes at all.
Among the states that do, some have uniform tax rates across the state, and some have tax rates that vary by county (or other political entity). Often the state declares a base rate, and then each taxing entity adds an amount to that. Where I live, the sales tax used to be smaller in the next county over, so people making large purchases would often go over there to buy things. Same for people who live in a state with tax but are close enough to a state without it so that they can cross over and buy there. This works for almost everything except items where the state gets involved in licensing and registration, such as cars.
Among the states that have sales tax, different items are taxed. Some tax clothing, some tax food, some tax only some kinds of food, some give time-limited tax holidays on certain items, some tax services and some don't and on and on and on. If you buy for a business you might not have to pay sales tax if the items are used in production, but if the items will be transferred to the client you do (I'll leave it to you to imagine the swamp that creating software as a consultant leads you into -- is it "tangible personal property?); if you're a not-for-profit then there will be different rules there, also.
Many states expect you to reveal out-of-state/online purchases to them, and after confessing, to pay the appropriate sales tax. Some people actually do this, but most don't.
So the tax-map in the US is an enormous patchwork of different rates and regulations.
As for internet purchases, it's also complex. States with sales tax will always insist on the tax when the vendor has a physical presence in the state. So were I to buy a Mac from the Apple website, Apple would charge me the appropriate sales tax for my state and county. Were I to buy it from another vendor, one who had no physical presence in my state, that vendor might or might not charge me that tax. This used to be the case for Amazon.com and New York state (where I live) but NYS passed a law requiring Amazon to collect tax, and although Amazon has filed some sort of protest, they have been complying. When I'm in another state and buy the identical item from Amazon, they don't charge me sales tax.
Sometimes people will buy online from a vendor within their state (and, online or not, that vendor should charge tax) but will have the item shipped to another state, thus avoiding the tax. Then they either go and pick it up, or have somebody ship it to them.
Complicated? Yes. And it's tricky even if you're the vendor (I was in business in NY State for a long time, and had to collect sales tax) -- for example, I had an onsite specialized data processing business, and although I might have done much of the work in one county and then finished up in the client's county, I had to collect and remit the tax appropriate for the client's county, even though the services were performed mostly in another.
Fun! Whatever VAT's flaws may be, at least it's easier. Isn't it?
