I assume you are a sole trader also.
The official response by most accountants is personal tax is not a business expense so does not belong in your manager business. The problem with that logic is income tax is a major bill for any profitable business so budgeting for it is imperative, particularly if income is varying. Doing so ensures funds are allocated up to 18 months earlier than just waiting till the tax department sends a bill.
A way to do it is modify your chart of account as shown
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At regular intervals estimate your income for the period. This can conveniently be done when other tax is paid such as quarterly by reading it from Managers Profit and loss. The estimate can be improved if desired by deducting 1/4 of your approximate annual depreciation.
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Personal tax can then be calculated. In Australia the ATO provides a Personal tax calculator. This amount is then transfered from “Owner’s equity” to “Tax income payable” by journal entry.
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Provisional income tax paid to your tax department is taken out of the "Tax income payable " account (In Australia this is done with each Business Activity statement, typically quarterly. Other components going to “Tax GST payable” and “Employee PAYG tax”).
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The running total of the "Tax income payable " account showing the difference between your estimate of your income tax liability and what you have provisionally paid to your tax department. The sign providing some guidance on how early you should submit your annual tax return.
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When your income tax is submitted, the actual tax bill/refund can be used to put in an adjustment which would clear the “Tax income payable” account at the end of that financial year with any residual going into / coming out of “Owner’s equity”. This is done when entering the tax Payment/Receipt into Manger by putting in a line item which is equal to the “Tax income payable” account at the end of that financial year but opposite in sign and paid into that account with any residual going into / out of “Owner’s equity”.