I'm European, so I better know the european side of american/european business. Between USA and Europe, when you trade service between enterprises, there is no VAT. And software is seen as a service. So, there is no tax payment. If you sell to individual customers, it is more complicated because there is VAT and you must manage it country by country, with different rates and terms. But as soon as you trade only with companies, there is no VAT to manage. But, there are very precise mentions to put on your invoices. Failure to put those mentions exposes you to pay the taxes. Anyway, don't worry about that: it is simple stuff for any accountant who deals with international trade. For the american side of your business, I'm not skilled at all to answer.