For anyone interested, here are the Australian coin values:
[200, 100, 50, 20, 10, 5]  # $2 and $1 are coins. We also have no 1c  
or 2c

This means I have to consider the case where it is not possible to  
construct the amount from the given coins, eg. $7.99

Nice to have one I could do in the ten minutes after breakfast while  
the kids get dressed :)

Cheers,
Dave