Okie, the ACE250 doesn't really tell the difference between zinc and copper pennies. It may a little, by hitting the lower edge of the penny range, where a copper cent read solid penny, but I've had plenty of the copper ones ring down there too, maybe if they're at weird angles in the ground or something.
I will basically dig anything that reads in the silver, copper, or gold/aluminum/nickel/foil range, and only dig iron signals if they are good, solid, repeatable tones.
I'd probably skip the zincs if the ACE250 were able to point them out well like your machine, but it doesn't. Oh well, a penny is still money! Anyone who doesn't want their pennies, send 'em to me, lol!