Whether you are retailer or wholesaler you might need to manage taxes in your online store. Magento allows to add tax classes for products and customers in Sales > Tax tab. In here you are also able to set Tax rates for products that will be exported to other countries (Import/Export Tax Rates) .
When you have set products tax classes, you may choose to display prices in catalog to include TVA or not. For that you need to set value for "Catalog prices include tax" in System > Configuration > Sales > Tax > Calculation.
When you define promotions in your store remember to define which prices it will be applied to: prices with or without TVA by setting "Apply Discount On Prices Including Tax". This is important because in some place your customers may end up with discount prices but TVA still calculated from the original price.