If the setting in your profile lists you as a non-taxable business, then you will be exempted from sales tax and it will not appear in your invoice. In the section “Information about the freelance occupation” in the menu item Account > Tax information, you must select “yes” if you are a small scale business; you must also specify your tax identification number and tick the “small-scale business”. This ensures that your invoice includes your tax number and that the sales tax is not specified. If you do not tick the “small-scale business” the sales tax will be specified.