I'll just pop in to say that taxing any religious institution is entirely idiotic and reprehensible. Such an idea can only come from the minds of those who are so ingrained in the blind materialism of our time that they can no longer see the inherent beauty and sincerity of religious striving. Churches (with the exception of the parasitic megachurches of charismatic scammers) do not function like businesses in any manner.
The RCC in particular is idiotic to target for two reasons:
1) Parishes function independently and are reliant on the tithes of their parishioners (this is shared with all other churches)
2) The RCC governs itself from the sovereign state of the Vatican, so taxing parishes would be tantamount to taxing a foreign embassy.