>>60904478
I can understand stacking pennies for relaxation or to create art, but for those who are stacking for profit here's how the numbers grind…
A pre-1982 US penny is 95% Cu, 5% Zn, and weighs 3.11 grams comprising 2.9545g Cu and 0.1555g Zn.
At the current price of $4.47/lb avdp for Cu, a penny has 2.91 cents' worth of Cu, and the zinc component adds less than 4 hundredths of a cent.
Wow! A potential instant profit of 1.91 cents of profit from each penny!
If your goal is to have a profit of $100 from the copper content in pennies, you would need 5231 pennies ($52.31) weighing 15.46 kg = 34.075 lbs avdp.

Going to sell them on ebay? Ebay takes a 12% cut of the sale price as a fee. You now have $88 in profit.
Unless it's for pickup, somebody is going to pay for shipping that 34.07 lbs. The customer will want to make up that cost - maybe by paying less for the metal, or you pay. That's another cut into profit.
Going to melt it yourself? You kind of have to – no commercial company in the US will do it for you: it's illegal there, and businesses have better things to do than risk their money, business, and/or freedom for the sake of melting your little stack.
>makeitfrommetal.com/is-it-illegal-to-melt-destroy-us-pennies-and-other-coins/
Bars you create can return the most profit. But you need to buy or make the furnace, fuel, molds, handling equipment, have the time and space to work with the stuff and create a product pretty enough to be saleable.
>https://www.youtube.com/watch?v=YPQDkKA4MLE

Tl;dr: You'll more likely end up with buckets of pennies sitting in the garage for the rest of your life, and your kids will curse you for leaving this mess.