For those that want to play there is a calculator at the bottom.
Weight of an ATACMS is 3690lbs and drag coefficient is below 0.7. Have to guess at the cross section, I put in 3ft. Gave a terminal velocity of 3100 f/s - between M2.5 and M3.0.
https://www.grc.nasa.gov/www/k-12/rocket/termvr.html
For those that doubt that missiles go supersonic on descent I refer you back to the Falcon 9 video and the double crack boom on landing - and that after burning back down range to the launch site and a long deceleration burn during the descent to reduce horizontal speed.to zero and reduce vertical speed prior to the last second landing burn.