Buying Nexus 4 across The Pond.

Here in the UK the 16GB Nexus 4 will be £279.00 exactly, which converts to about $444. Now, the US version will be $349, which is obviously far cheaper. Although, as I understand it, sales tax gets added on to that price.

Now, I have family in the states who I am visiting for Christmas, so it would be fairly easy to order one and get it delivered to them. How much is sales tax and how do I work out what the final price will be? They live in St Louis where sales tax is 8.491% (I think), so does that make it $379 or do I need to add on state tax or something else too? Americans make buying stuff difficult :P

And finally, apart from the mains adapter for charging, will the phone + extras be exactly the same as one I would buy in the UK?

Thanks for your help, and I can't wait to bring back heaps of Reese's Pieces :)