The IRS closely scrutinizes the common person, it should certainly show at least the same amount of attention to the political parties which claim to represent all of us! Campaign contributions and political funding is a murky grey area as it stands, and it could use a strong dose of transparency and oversight.
It's a danger to liberty to give the IRS a right to decide who to tax because of their beliefs, whether political, religious, or what have you. It violates freedoms of speech and religion. As Thomas Jefferson once said in his famous legislation on religious freedom, the Virginia Statute for Religious Freedom:
"That the impious presumption of legislators and rulers, civil as well as ecclesiastical, who, being themselves but fallible and uninspired men have assumed dominion over the faith of others, setting up their own opinions and modes of thinking as the only true and infallible, and as such endeavouring to impose them on others, hath established and maintained false religions over the greatest part of the world and through all time...
That to suffer the civil magistrate to intrude his powers into the field of opinion and to restrain the profession or propagation of principles on supposition of their ill tendency is a dangerous fallacy which at once destroys all religious liberty because he being of course judge of that tendency will make his opinions the rule of judgment and approve or condemn the sentiments of others only as they shall square with or differ from his own"
If this applies to the judiciary, it should likewise apply to the IRS. They will restrain opinions that differ from their own, and tyrannically assert their own beliefs upon others.
No, I do not think that the IRS should scrutinize political groups and I think that takes the power of the IRS way too far. The IRS should be a functioning group that exists to check on people's tax returns to make sure that they are true and valid, and stay out of politics.