In practice, any coin issuing entity will make coins in such a way that a greedy algorithm is optimal. That is, noone is issuing coins as 7c, 6c and 1c coins (a case where greedy isn't optimal to make 24c change (greedy gives you 3 x 7c + 3 x 1c, while optimal is 4 x 6c)). Instead typical coin denominations are 1c, (2c), 5c, 10c, 20 or 25c, (50c), 100c, (200 or 250c), (500c). For instance, US dollar coins come in 1c, 5c, 10c, 25c, 50c, and 100c; Euro coins in 1c, 2c, 5c, 10c, 20c, 50c, 100c, and 200c; Yen coins in 1y, 5y, 10y, 50y, 100y, 500y; Pound Sterling coins in 1p, 2p, 5p, 10p, 20p, 50p, 100p, 200p (effectively the same as Euro coins). For all, a greedy algorithm is optimal.