I believe when you get to know your machine (no matter what it is) you can tell the difference in "sound" on nickels and other coins against trash/etc. (I know I can). I can hear the difference in a new penny (zinc) compared to an old copper penny. I can tell with almost 100% accuracy the difference between pull-tabs and nickels just by the sound of them. Nickels have a strong even consistent solid sound while pull-tabs will have a higher, broken up sound. Zinc pennies are the same way, they have a broken sound and are a higher pitch, Quarters are solid, loud, even, strong and consintent (as is any silver coin) and dimes are the same as quarters but, the length of the signal is shorter?
Takes many a yrs to get to know/discern the difference in sounds in this manner. And although I'm not, and it's not 100% accurate (as nothing about metal detecting is, including the machine itself) -? it's dam close! When I dig a 'nickel sounding signal' - 8 out of 10xs - it's a nickel! I pass over zinc pennies and leave them for others! I have dug 1000s of them and with an accuracy rate in the 99% range, I am confident in doing so! I do dig the 'copper' sounding pennies (especially when) I'm hunting an old site.
It all boils down to "time, practice in the field and experience" with your machine/s.
Don't get me wrong though, I have seen newbies out detect pros before and make some good finds, more finds, etc. (but on a consistent basis?) not even close!
One example,
I took my friend Jeff (not you moderator jeff!) to a beach on an old lake back in the woods off the beaten path, and in 10 minutes, he found a 1921 Morgan dollar in 3 inches of sand on the beach. When all was said and done, he came away with the Morgan, 2 silver washingtons, some wheat's and a bunch of newer clad junk, and all I found was 1 silver Roosevelt, and some clad.
Moral of the story!?
Since all he has for a detector is a GTAx 1000 and had to work the next day,
I took my Fisher CZ20 out there the next day and got in the lake (because I knew when he found that Morgan, that the lake had never been detected) and I cleaned up!!!?

? ?Gold rings, silver rings, necklace's, pendants, medals, wheat pennies, silver coins from the 1800s/1900s and 100s of other coins & cool items!
Needless to say, when I showed him all the finds I made, he about hit the roof!
Still can't convince him to UN marry that GTA and get a good water machine though (and he's NEVER out done me since that 1st day together, which was like his 3rd time ever metal detecting) and that was 4 yrs ago! lol?
