This video has been going around (HT - Robert Murphy). If it looks appealing to you, it's a little misleading in a couple ways. First, although the transactions tax seems low, you've got to remember that the volume of transactions that goes on is many multiples of the actual size of the economy, so a 0.05% tax on a transaction is a lot bigger than a 0.05% tax on income.
The virtue of these sorts of ideas is that we think that some speculative activities can impose large costs on innocent bystanders (anyone remember 2008?). If you tax it you get less of it and you reduce the likelihood of a crisis. The problem is there's lots of good speculative activity too - informed speculation on the future prices of assets helps us make reliable decisions about the future. I've got two hypotheses that I think are likely to be true but I don't know for sure: (1.) the volume of responsible speculation is usually a lot bigger than the volume of irresponsible speculation, and (2.) the profits earned on responsible speculation are a lot smaller than the profits earned from irresponsible speculation. That suggests this sort of tax would do a lot more to discourage good speculation than bad speculation.
We can talk about transaction taxes or "Robin Hood Taxes" again when we figure out how to only tax bad sorts of speculation (this is a dismissal of the idea - not an encouragement for politicians to go around deciding what is and isn't responsible!).
I'm not saying taxing the well off to help the worse off is a bad idea. It's a great idea. It's just not clear this is the way to do it.