The tax deductibility of projects depends on where each Worthy Cause is listed and in which country they have registered charity status in.
Filter the tax-deductibility of projects by country by using the blue 'Advanced Search' filter on the project listing page. In your B1G1 account, you can also generate a tax claim statement that gives you a list of contributions you've made to organizations that offer tax benefits in your country. However, as tax claim requirements vary widely across countries, please contact your own tax advisor to ascertain the tax deductibility of your contributions.
If you're a US registered business, you will be able to receive tax deductibility when you give to any project on B1G1 as B1G1 Giving is a registered 501(c)(3) nonprofit in the US.