From a distance, Australia's tax system looks gender neutral.
The tax return carefully avoids gendered words and the tax rules were purged several years ago of direct gender discrimination. There is no assumption that the male in a partnership is the primary breadwinner or that the female is the primary carer.
There is no assumption that one partner must disclose to the other all their financial affairs to enable a tax return to be sent on behalf of both of them, unless they explicitly agree to it. Single men and women are not treated differently for income tax purposes.