Yes, they do. For some people, the bitter taste of tannin is pleasurable. However, as always, people react differently to various food components, and for some, tannin might cause headaches. They also seem to lower blood pressure, reduce the risk of cancer, stimulate the immune system, and have anti-bacterial properties.
We do not have the information about the percentage of Tannin in our Teas since no testing has been done. Generally the levels of Tannin in this type of product are not significant and therefore quantitative testing is often not done.