The PDF Invoices are completely useless in their current form even on magento 126.96.36.199.
Whilst it is relatively straightforward to tweak the emails to display correctly, it is extremely difficult to get a PDF which will correctly display GST or EU tax for that matter.
The invoice lines should read (with the rounding)
Products SKU Price Quantiy GST Subtotal [INCLUDING GST]
Widget WD1 9.09 1 0.909 10.00
Shipping (inc GST) 10.00
GST included 1.82
Its not a matter of editing invoice.php or abstract.php, these only call arrays - which for some reason are different to those used to generate emails and display (correctly) in the back end.
It appears it is impossible without going into the tax model in some depth to modify the Item line subtotal to include GST.
Surely someone has found a way around this?
Unfortunately there is only one extension which remotely addresses this (for EU which is similar enough to moify for Australian purposes) - PDF invoice for EU region by no stress commerce which is both pricey and has an odd Cezch website.
This is really a flaw in Magento design for places that use tax calculations.