All around rifle

So I found a great deal on a .270. I got a Marlin XL7, which I understand is an entry level rifle that got all of the basic stuff right, but I also know that Marlin is currently not serviceable, as they were recently sold to Ruger after Remington bankruptcy. I am now looking at a scope and hear that 3-9x40 is pretty standard for TX whitetail hunting. How important is parallax settings?