xc7621:
Country set to NZ. Created a new zone as NZ. And modified the original zone definition and associate country NZ and zone NZ.
Here is an example of output when checkout use a test accoun (NZ customer, purchased an phone $599 incl GST):
Your Total
Sub-Total: $599.00
Flat Rate (Best Way):$10.00
NZ GST 12.5%:$66.56
Total:$609.00
It seems the GST is wrong as well.
How is this wrong ?
Your tax-included price is $599.
The tax included in that price is $66.56
$599 + 10 = 609.00
So, the question then becomes: should your shipping also be taxed? If so, then you'll need to edit your shipping module settings and associate a tax class (ie: Taxable Goods) with it, instead of --None--.
Otherwise, I see nothing wrong with what you've got.