I do not know for sure but imagine it goes something like this. Google use an automatic currency conversion program based on the same rates the banks use (or similar). Then, all bids are converted into a base currency, e.g. US$, and the calculations for ad position made. When a click is made the CPC is calculated in that base currency and then converted back into the advertiser's currency (rounded up to the nearest minimum unit in that currency). Therefore, the base CPC is the "same" for all advertisers. The only benefit might come from the rounding process depending on your currency - but it is probably only going to be significant for high turnover accounts. If that benefit exists it is likely to be greatest for bidders with the lowest value base currency unit, e.g. Kenyan shillings, indonesian rupiah, (if you can bid in those currencies) that are only worth tiny fractions of a US cent.