Here is my attempt at this:
$5,$10,$20 =(14, 1, 1), (12, 2, 1), (10, 3, 1), (8, 4, 1), (6, 5, 1), (6, 3, 2) =6
$5,$20,$10=(10, 2, 1), (8, 2, 2), (6, 3, 1)=3
$10,$5,$20=(6, 4, 1), (5, 2, 2), (4, 4, 2)=3
$20,$10,$5=(3, 2, 4), (3, 3, 2)=2
$20,$5,$10 =(4, 2, 1)=1
Total Change =6 + 3 + 3 + 2 + 1=15