easy way to tell how much this is costing you is o note your account balance at the start of the day , how much it drops when you buyin to your first table so you can get a rough idea of the exchange rate, then at the end of your session in the ipoker software click on the my account option and then go through the cash table history and add up all your buyins ,all your cashouts and find the difference. convert that at the exchange rate from the first buyin,add to your starting balance and compare with the actual balance at the end of your session. The diference will be how much this currency rounding has cost you in that session , and should be relatively easy to then multiply up to give you monthly and annual costs.

sample size will obviously apply so the more days you do this over the more accurate the answer will be.