The Transaction List by Supplier report will generate all transactions linked to each supplier in your QuickBooks Online account. The totals displayed in the Amount column are inclusive of tax, and if you'd like to see the tax breakdown, you can customize your report by clicking the small Gear icon, click Show More, and check off the box next to "Tax Amount". You can also select "Net Amount" if you'd like to see the total before taxes. 

This is useless as many of our subcontractors have 10-20 invoices and there are 50+ subcontractors...it would take too long to add all every line of sub total and tax up.

Otherwise, you can run the Expenses By Supplier Summary to generate the totals. 

This option doesn't create a total that includes GST...so still not a viable option.

There must be an easier way!!!