When you have a valid European VAT number outside of the Netherlands, and you are having your purchases delivered to a place outside of the Netherlands you can use the 0% tax option. Simply enter your VAT number during checkout and you will automatically get a total price with 0% tax. Do note that if you pick goods up yourself in the Netherlands you will still have to pay 21% VAT which you can request back from your local tax service during your normal VAT reporting.
If you purchase from outside the EU you can always get a 0% tax invoice (so you do not have to pay salestax) provided that there is proof that the goods did leave the European Union (when we ship the goods to you this happens automatically).