I do not normally rant, but tip4commit and its ilk are some of the most infuriating people in the world to deal with, since they're opting other people's projects into something that has all sorts of legal/taxation consequences and think that "we have no way to remove you once you get opted in" is an acceptable answer. I'd push complaints further up to GitHub, since I'm sure something in the way this works violates t…
How can there be taxation consequences unless you act to set up a bitcoin address and accept the offered tip? If you've done all that, I think it's clear you know what you're doing. If you don't do that, then the money (apparently?) returns to the project you committed to, from whence it came. The only way there could be tax is if you receive the money, and that can only happen by you deliberately becoming involved.
See IRS publication 525, page 2, "constructively received income": http://www.irs.gov/pub/irs-pdf/p525.pdf
There's some fuzziness and legal room here but the safe thing would be to declare it as income.