Or more than likely, the third party, FastSpring, that handles the transactions for Stardock. They are the ones changing the currency for me to €uro and there is clearly no need for that when using PayPal other than FastSpring charging an exchange fee.
Sales between USA and many other countries (mostly EU) required that a Value-Added Tax (VAT) be collected. We had not been collecting them in the past but we are required to do so. Because of the high costs of administering VAT and other reasons is why we switched over to using FastSpring to facilating our sales.
So, with VAT, State Sales Tax and Currency Exchange rates, the prices will vary from Country to Country and State to State.