howdy

"The problem is too hard or we're too busy to try and solve it." Thanks for an honest answer.
"42" Obviously always a good answer.
Approximation#1 If 2300 pennies fit ($23.00) then 2300 nickels would be $115.00 and 2300 dimes would be $230.00 - which would only be true if all coins were the same size. But not a bad guess.
Approximation#2 volume of Oban cylinder = 1.638 million mm(cubed) and volume of penny = 441.79 mm(cubed) so if pennies could pack perfectly without any wasted space then 3707 would fit. But since only 2300 fit, that means the coins take up only 62% of the volume and the rest is air. If the same factor applies for other coins, then 1474 nickels would fit ($73.70) and 2986 dimes ($298).
Approximation#3 the packing factor will be slightly different for nickels and dimes, but the effect will probably be small. And you'd need to run computer simulations (or do the actual coin-filling experiment) to measure it. Exercise left to next semester, when students' brains will need their exercise.