I don't think we have any service in place today who deduct upfront tax amount from the bitcoin exchange. So all exchange procedure is tax free. It's on the owner of that amount who has the legal obligation to declare that amount to the tax authorities.

Also I am sure it will be illegal to evade tax. So I personally won't encourage to have such services to come into existence. Majority of the governments are already against crypto currency. So if we have any such illegal service running openly, it will further damage the reputation of Cryptocurrency.