https://en.wikipedia.org/wiki/Taxicabs_of_the_United_States#... says there are 1825 cabs in Boston. Boston is 10% of Massachusetts' population, so let's say there are 18k cabs in the state.
http://www.reuters.com/article/us-massachusetts-uber-idUSKCN... says 5 cents/ride-hailing app will go toward taxis, and Uber+Lyft do 2.5m rider per month.
So, the tax will produce 2.5m rides/mo * 12 months * 5 cents/ride = $1.5m/year.
That works out to... drum roll... $83 per taxicab per year. How is this supposed to help taxi drivers with anything? Maybe as ride-sharing increases, this becomes $200 or $400 per cab per year, but that's still a small sum. I imagine a few hundred dollars is a small consolation when you lose 50% or 90% of your business.