Like Paypal, Google has also added a Statement of Monthly earnings that can be accessed from the Payment History tab of the Adsense control panel.
Though you cannot export it in Quickbooks or other formats, print a hard copy and attach it with your Tax returns. The statement has all the earning details for the previous month including the currency exchange rate at which the payment was issued by Google.
Tricks of the Trade: If your local currency is getting too strong against the US Dollar (like in India where the Rupee is at a seven year high), you can issue a self-hold instruction to Google.
Next month, if the exchange rate gets better, remove the hold payment instruction and Adsense will issue you a check of accrued earnings using the currency rate prevailing at that time.
The risk is that if dollar weakens further, your earnings will be reduced even more. Also, Google won't pay you interest for the accrued earnings.