Display USD & AUD but charge USD in the backend

Hello, I have a USD company that sells to Australia.
What I am wanting to achieve is that the customer sees the products in AUD, but is then charged in USD.
IE;
Product ‘X’ is displayed as $209 AUD (if they chose to click USD it would show $131.46.
Customer views cart and checks out, product ‘x’ total is $209 AUD and the are visually charged $209 at the cart checkout.
We want the back end to be charged as $131.46USD as our site is set up in USD.
We will insert text somewhere stating that they will be charged in USD.

THANK YOU