Towboater, Do you mean zinc pennies? Or copper pennies ?
I would be careful with using the "learn" edit. Instead, I would use the manual edit. The reason is: As we all know, when you wave a target around in an air test (so-as to cause the machine to "learn" what to notch out), that there's frequently the occasinal "bounce" left or right, up or down, etc... (like if you didn't have an exact centered swing, or for a moment, held that coin at an angle, etc...). So you would, in effect , be causing the machine to "learn" a spot that you didn't necessarily want it to learn. So instead, a person can just swing a penny a bunch of time, learn the spot on the screen that it "most normally" come up at, and then just black out that area on the screen manually. You know, not just a single pixel, of course, but a little blotch of pixels right around that spot.
And yes, as Dew says, you could accidentally also notch out something wierd, like a VERY big men's college or super bowl ring. Or a $20 gold, etc.. But ....... heck, ... "what are the odds"? haha If we're all brutally honest, in all our years of detecting, the ratio of pennies to those rare targets is ... ?
Also I would point out that you're probably also going to miss clad dimes, and silver dimes, if you meant copper pennies. But if you meant zinc pennies, then no, you're not going to be passing copper pennies, clad dimes, etc...
I often-time pass surface pennies, but still chase deeper penny signals (if you're in stratified turf, where it's reasonably certain the shallower stuff is new, while the deeper stuff is older). Or at the beach, when ferocious storms have caused severe erosion, leading to targets "as fast as I care to dig", then there too will I sometimes (gasp) pass pennies. Just by sight/sound though. Not by editing them out. Because by the end of the day, I will simply not have exhausted the amount of targets on the beach (I will get chased out by the incoming tide). So it stands-to-reason my time is better spent chasing the low conductors (higher likliehood of being gold), than the high conductors (higher likliehood of being clad). But alas, those days are few and far between