I am from the Southern United States (though I don't believe this is, specifically, a southern tradition). And I was taught to make a wish while tossing a coin in a fountain. Is this a recent tradition (we now have the ability to build fountains where we choose to more easily) or does this have earlier origins?
The wishing well found a famous expression in American pop culture with the 1937 film, "Snow White". No coins were sacrificed in the Depression-era film, but the idea of the wishing well was nevertheless embedded internationally and would have been understood by most audiences in America and Europe.
The idea of casting something into water - a fountain or a well - to procure good fortune courtesy of a supernatural entity or force is extremely old. Water apparently has a millennia-old reputation as a liminal space - a transition from our terrestrial existence into something else, and that "something else" was often perceived as being a gateway to powerful forces.
While we can see prehistoric evidence of "sacrifices" in bogs and ponds, wells and deep springs provided an exaggerated sense of the liminal by being both water and an access to the depths of the earth. I placed "sacrifices" in quotes because in the prehistoric context, we can't be sure what was happening, but the many artifacts (and occasionally people) which were clearly placed into bodies of water (or bogs) appear to have had some ritual significance. European ethnographic observations combined with primary source documents reinforce this perception that placing objects into bodies of water for leverage with the supernatural is an extremely old practice in Europe.
The natural springs at Bath, England, for example, appears to have attracted prehistoric attention. It was then recognized as important during the Roman occupation. Although it was attractive as a source of healing water (bathing and drinking), retrieved artifacts also point to a long tradition of sacrificing valuables to procure favorable results.
European folklorists describe conduct that one should use when engaging the supernatural at a well. This includes walking counterclockwise around the well three times and then casting the coin backwards over the left shoulder. The folk, however, are often inconsistent, and some would abhor the idea of walking in a counterclockwise fashion (against the sun), so looking to folklore for consistency can be problematic. Those who wish to procure favor from the supernatural - to win a wish - may just as easily offend the forces, which are notoriously capricious. You may simply lose your money.