It's no fun when you don't explain the reasoning.  Here's the reasoning:
Since the amount is 68 cents you must have exactly 3 or 8 pennies,
but you can't have 8 pennies, so you must have 3 pennies.  So
the problem simplifies to making 65 cents with 4 coins.  So you'd have
to have a half dollar or 1 or 2 quarters because 4 dimes isn't but 40
cents.  If you used a half dollar, then you'd have to make 15 cents with 
only 4 coins with only dimes and nickels.  You could do that with 3 nickels,
but that wouldn't be but 7 coins, one short of 8.

HEY!!!  A light just dawned.  If we swap the half dollar for two quarters,
that'll still be 65 cents, and 1 more coin, or 8 coins!  By golly that's
it!

That's the answer!  2 quarters, 3 nickels and 3 pennies.  

Just to complete the problem, we must rule out all other possible answers.
Any other possibility would be to use only one quarter.  If we had only 
one quarter, we'd have to make 40 cents with 5 coins with nickels and dimes.
And there is no way to do that since the closest we could come is 4 dimes
and 2 nickels.  But that would be 6 coins not 5. So there's just one answer:

2 quarters 3 nickels and 3 pennies.

Edwin