Yes, your KiwiSaver money is taxed, but only your investment gains are taxed. All of your own contributions, and your employer’s contributions (after ESCT), are deposited into KiwiSaver as tax paid capital.
Your returns/investment gains are usually taxed as per the PIE tax regime, with interest or dividends your fund generates being taxed at your prescribed investor tax rate (PIR). You won’t need to worry about paying your KiwiSaver tax, as your KiwiSaver provider will pay this automatically for you.