A lot. ;)
The answer will depend on pennies from which country!
50
12
Assuming that the 14 inch box is square, you could fit a circle inside with a 14 inch diameter.
91 with .79 cubic inches to spare.
1,728
729 of them!
1,000-3,000 pennies
60 - 70
50,000
To fit 5,000 pennies, you would need a box that can accommodate approximately 25 pounds, as 5,000 pennies weigh about that much. Given that a penny has a diameter of about 1.9 cm and a thickness of 1.52 mm, the volume occupied by 5,000 pennies would be roughly 1,000 cubic inches. A box measuring around 12 x 12 x 12 inches would be sufficient to hold the pennies, allowing for some extra space.
The answer will depend on the country whose pennies you have in mind. Since you have not shared that crucial bit of information, I cannot provide a more useful answer.