i dont know what the grading is like in new zealand, but in the US this is the grade spread generally:
4.0=A
3.7=A-
3.3=B+
3.0=B
2.7=B-
2.3=C+
2.0=C
1.7=C-
1.3=D+
1.0=D
0.7=D-
0.0=F
So someone with a 3.3GPA has an averaged total grade of B+...keeping the above conversion in mind, it's easy enough to figure out your GPA (though keep in mind the amount of units too in your calculations).
If you're looking to get into grad school over here you should have at least a B average (3.0)...and for top schools at least a 3.5