you would need a device that can measure the temperature of each side of the coin simultaneously.
There won't be any temperature difference between sides, metals are excellent heat conductors.
pennies these days are made of mainly zinc like 95 percent with a copper coating. zinc is not quite as good of a heat conductor as copper.
lets say room temperature is 85 deg F and your hand is 95 deg F. That's a temperature differential of 10 degrees. You have the coin sitting in the palm of your hand with one face exposed to 95 deg F and the other side exposed to room temperature. There is going to be some temperature differential when you actually toss the coin and the sides will not get into thermal equilibrium before the coin lands.
So what i'm saying is the way you hold the coin and how long it is in contact with your hand and in what way those things can have an effect. probably not large ones but i haven't tested it.