Same currency on Invoice

[xxxadrenalinxxx]

Hi everyone,

I need all the invoices printed out via order printer to show the total order sum in AUD regardless of how the customer paid. Is there a way to add a line of code that will automatically retrieve the total amount of the order in AUD? Or even to calculate all the items ordered in AUD (sum is calculated via adding up order total instead of currency). 

I hope this makes sense, I have been trying everything and scouring these forums to find an answer. Any help will be appreciated. 

Regards,

Mark