The gimmick here is that there are three coins, ranging in size from a regular penny to a huge novelty penny. Clever handling throughout the trick, however, makes them appear to be the same coin increasing in size.
The largest of the three pennies is placed into one of the performer's pockets, and the second largest in his other pocket along with the magnifying glass. The regular penny is in his hands when he starts the trick. He draws his audience's attention to the penny by flipping it over a few times in the palm of one hand using the fingers of the other. He will then say that, since the audience probably can't see the penny very well, he's going to get out his magnifying glass.
The magician will palm the regular penny in the hand going to his pocket, but naturally close the other hand as though it's still in there. He reaches into the pocket with the larger penny and magnifying glass, withdrawing them both after dropping the regular penny. The larger penny can be easily concealed in his fist since the audience will be focused on the magnifying glass. Remember that his other hand is still in a ball as though concealing the original coin.
Fluidly, he brings his hand with the magnifying glass to his other hand. As he opens the hand in which the audience thinks he still has the penny, he quickly drops the larger coin into it. He does this so the audience is seeing the new larger coin through the magnifying glass. He moves the magnifying glass away from the penny, pointing out how the penny appears to be getting larger. He then reveals that the coin actually has increased in size.
The next step for the magician is to casually move the magnifying glass to the pocket (ideally a back pocket) containing the largest coin. Since the magician is done with the magnifying glass, it makes sense that he would be pocketing it. Plus, the audience will be too amazed by his previous reveal to note that he's putting it in a pocket different than the one he took it from. He deposits the magnifying glass and takes out the big coin.
The largest coin is kept concealed in-hand by his side as he manipulates the second coin with the other hand to distract the audience. The magician squeezes the second coin in a fist and gives it a flourish. Then, he pretends to throw it into the other hand by keeping it palmed but flicking his wrist. Simultaneously, his other hand is brought up quickly to reveal the large coin. If this is done fluidly, it will appear as though he threw the biggest coin from one hand to the other.