Facially Unconstitutional.
"Indeed, this case involves a more disturbing use of selective taxation than Minneapolis Star, because the basis on which Arkansas differentiates between magazines is particularly repugnant to First Amendment principles: a magazine's tax status depends entirely on its content. Above all else, the First Amendment means that government has no power to restrict expression because of its message, its ideas, its subject matter, or its content.
... In order to determine whether a magazine is subject to sales tax, Arkansas' enforcement authorities must necessarily examine the content of the message that is conveyed.... Such official scrutiny of the content of publications as the basis for imposing a tax is entirely incompatible with the First Amendment's guarantee of freedom of the press."
Arkansas Writers' Project, Inc. v. Ragland, 481 U.S. 221, 229-30 (1987), Internal quotations and citations omitted.
I agree. In theory this would be an FF move to take on the ugly porn industry but this law could easily extend to explicit music or literature that isn't at all commercializing acts of sex.