No sales tax is collected on Balsamiq purchases.
Balsamiq Studios LLC only has US sales tax nexus in California and Illinois. California sales are exempt from the sales tax, because the software is delivered through electronic means. In Illinois, Balsamiq bears the burden of the sales tax and remits the appropriate amounts to the State.
If you live elsewhere, please consult with your tax advisers regarding the need to self-assess the use tax on your purchase.
You can find a copy of our W9 and other tax-related documents here.