Id check with the NZ customs about taking it in though. Are you traveling on a work or visitors visa. That might make your reason for taking the sharps as tools to earn money and will lead to more questions.
Best advice I have seen. don't take a risk. it takes nothing to check, and they are very helpful. if you do by email and print the email off and take it when you go. it provides an extra level of proof that you have complied with their regulations.