Tax that never adds up - what to do

So I have three sources of employment:

Two salaried jobs which are basically 50/50 in time/salary.

These aren’t accurate figures, but pretend one job earns me $55k, and the other about $55k

I can only apply for tax free threshold on one job: so one job takes out $7,945 tax; and the other takes out $10,850

This makes for total tax paid on $110,000 of $18,795.

But tax on a total income of $110,000 should be $26,820. Because my income is split from two sources, I’m $8,000 short of what I should have paid.

Compounding matters, I do a bit of casual work which I invoice for using Hnry. Hnry takes tax out of that extra income, assuming I’m earning $110,000 + whatever extra I earn - so Hnry’s calculation is “accurate” for the extra income at tax time, but of course it’s not enough to cover the shortfall created by my two salaries.

I try and claim expenses to reduce my taxable income and owed tax, but it’s never enough and I still always end up with a tax bill at the end of the year. Given some recent pay rises, I suspect this will be my largest bill yet this year…

What would be the best way to structure all of this so as to minimise the “surprise” bill at tax time, which I’m realising is not a surprise at all, it’s just going to be the way it is unless I do something about it - I’m just not sure what the best options are…