The IRS stated that they could resolve the problem since anyone outside the United States on April 15 automatically gets a two-month extension. (Even though "legally, no one has ever decided whether a journey into space technically counts as leaving the United States.")
Of course, Apollo 13 soon had problems that pushed aside any concerns of tax filing.
NY Times report: https://www.nytimes.com/1970/04/13/archives/apollo-13-coasts...
Mission transcript: https://www.nasa.gov/wp-content/uploads/static/history/alsj/...
At least the customs requirement has been resolved: https://www.flexport.com/blog/apollo-11-astronauts-cleared-m...
That gave me a good laugh. Shouldn't it definitely count? You're zipping over every country on earth while you're in orbit so you definitely left!
But if you take off and land in the US, did you _really_ leave? You don't go through customs and immigration for every country you fly over when you're in an airplane, and generally aren't legally considered to have "visited" them. So, wow, good question.
The Kármán Line is also generally accepted to be the boundary of outer space, set at 100 kilometers above ground.
The ISS orbits at something like 415km above Earth.
I'm no lawyer but is seems plausible to say no, orbiting above 100km of altitude over the USA would not be considered entry into the country.
edit: I have to admit my reply was a bit dismissive but can someone enlighten me: Surely you have to be able to pay someone else to file your taxes for you, right?