We used to shoot tacks on a board at our Rondy, but now shoot shotshells that are held in a piece of coroplast, case head towards the shooter. The shell must disappear from the board at the shot, after calling out the number ie: A1 to about H10 - the letters A through about H run across the top and numbers 1 through 10 down the side. It's a fairly easy target, however some have difficulty with it. Depending on the rifle, you normally have to aim at the top edge of the shell's head to hit it.
When we shot tacks, a small bore hit right on the spot would leave a hold no bigger than the tack's head giving the illusion the tack was still there. I've seen more than 1 shooter, myself included, shooting at a hole. When placed at 15 yards, it is not an easy target, similar to string cuts, ball splits on an axe to hit 2 clay birds, one on each side as well as card splits.
Paul Mathews mentions his friend and gun smith, shooting tacks with a breechloading buffalo rifle which was loaded from the muzzle using heavy charges of powder and paper patched bullets - at 100 yards.
Many people use the term "tack driver' merely to embellish the traits of a rifle they are attempting to sell, of course. Tack-driver describing 'extreme' accuracy.