Here is the text of the first amendment since you seem to have difficulty remembering it:

"Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances."

Taxing a church or religion would fall under the prohibition of "prohibiting the free exercise thereof"

SCOTUS has looked at the issue 1 time and smacked down the thought of government taxing religion as blatantly unconstitutional measure.