Generally "Tac" channels are mostly used for unit to unit communication. They may or may not always be monitored by a dispatcher. They also may or may not be "repeater-ized". I can't say that is the use in Calloway county, but is pretty much the norm.
Having said that, I grew up in Minnesota. My first winter here was kind of cold. As people were gathering up their hats, coats and gloves, I heard someone say "Please hand me that 'tobbogan' over there". I was looking around for something made of wood, having a curved front end and used for sliding down a snow covered hill. Little did I know then that around these parts, a tobbogan is something that keeps your head warm.
So I wouldn't take what I think Tac means as gospel. I'm sure if you asked a local emergency responder, they'd be happy to explain what it is, and how its used.
Also, though I doubt this was the usage, but on Pierce fire apparatus TAK IV is their brand name for a front suspension on a fire truck.