Personal Gifts to Australia

I have for many years been sending Christmas and personnel gifts to family in Australia via Royal Mail without any problems. Their postal rate has increased dramatically so trying to use DHL but they have requested that I use product tariff codes ?? None of the parcels or gifts fall into the duty to be paid or restricted items so do I need to use codes or how do you tell which codes to use as for example T shirts are woven and not knitted or crocheted ??.