If you're a New Zealand tax resident, you pay tax on interest and dividends you earn from bank accounts and investments in New Zealand and overseas.
If you earn interest from New Zealand, your payer will usually deduct resident withholding tax (RWT) before they pay you.
If you get dividends from a company, your dividends will usually have imputation credits attached. You use these imputation credits to pay tax on your dividends. The imputation credits represent income tax paid by the company.
If your dividend is not fully imputed (not enough company tax was paid) then resident withholding tax should be deducted.
If you get interest and dividends from overseas, there are different rules depending on your situation.
If you are not a tax resident, you pay tax on investments you have in New Zealand.