Help!! Paypal Currency/Amount Mismatch

I hope someone can help me please! My online shop version 1.3.8 which I have recently upgraded calculates prices in $AUD as default but also collects $US, GBP and EU. I have installed PayPal IPN - Website Payments Standard module for my payment transactions and have chosen Selected Currency as my Transaction currency. However for all my $AU payments, (other currency total amounts are correct) Paypal has been miscalculating totals and collects different amount to the order total. In an example log file it says

Dec 03 2008 5:58 -- IPN WARNING :: Currency/Amount Mismatch. Details:
PayPal email address = [email protected]
| mc_currency = AUD
| submitted_currency = AUD
| order_currency = AUD
| mc_gross = 232.45
| converted_amount = 233.75
| order_amount = 233.75

So instead of receiving 233.75, Paypal transaction is receiving 232.45. I've only just realised this, so for my whole month of sales I have received incorrect amounts. Can someone head me in the right direction please. Thanks in advance

Ok, I think I have pinpointed the problem but don't know how to fix it. I have tax added to my shipping amount and it looks like Paypal is not adding the tax amount to the order total in the transaction. I have basis of shipping tax set to billing in 'My Store' and 'Payment module'. Any ideas on how to fix this?