You can activate AUD in standard and ipn modules by following this procedure.
Go to Admin/currencies and add a new currency australian dollars if it is not already there. AUD is the currency code.
Also go to Admin/modules/paypal_ipn or paypal(standard) which ever the case may be to accept selected currencies.
Now for Paypal IPN
Edit \catalog\includes\modules\payment\paypal_ipn.php file
from
if (!in_array($my_currency, array('CAD', 'EUR', 'GBP', 'JPY', 'USD'))) {
$my_currency = 'USD';
to
if (!in_array($my_currency, array('CAD', 'EUR', 'GBP', 'JPY', 'USD', 'AUD'))) {
$my_currency = 'USD';
For Paypal standard
Edit Edit \catalog\includes\modules\payment\paypal.php file
from
if (!in_array($my_currency, array('CAD', 'EUR', 'GBP', 'JPY', 'USD'))) {
$my_currency = 'USD';
to
if (!in_array($my_currency, array('CAD', 'EUR', 'GBP', 'JPY', 'USD', 'AUD'))) {
$my_currency = 'USD';
This way customers choosing currency as australian dollar can pay in AUD using paypal. Any problems please email me.