No. There are too many issues. First of all the UN is dysfunctional in terms of making policy, so any tax at this point would end up being absurd and ineffective.
Second, the UN has no real authority over any nation other than what is defined by treaties and what not, so there is no legal mechanism for this.
Third, there is too much division between the nations on how they want to do things. I mean we can't even get a baseline on human rights and democracy for the rest of the world, and citizens in some regions like the middle east probably don't even want it. So until we can get some common global understanding about what I believe are societal basics, the UN will never be able to do its job well.