Each country has their own rules and laws relating the collection of taxes from items purchased over the internet. Where I can I take the burden of this for you my international customers but in some cases it's just too damn hard. So... you're on your own. If you need more information on what to expect I hope these links are useful to you.
Canada - Importing by Mail or Courier
New Zealand - Send and Receive Items from Overseas
United States - Internet Purchases