It's due to the VAT (Value Added Tax). The list price on our store does not include VAT. VAT is a general consumption tax assessed on the value added to goods and services and is borne ultimately by the final consumer. If you have the privilege of VAT Exemption, please enter VAT Exemption ID at the checkout.
Tip: There is a special procedure for US organizations to place an order without sales tax only if our e-commerce provider receives proof of tax exemption prior to order placement. In other countries, such as in Europe, you can just enter your VAT number in the order form to learn more details.