Add method to round a given amount of money to the nearest possible amount of cash (aka Swedish rounding)
Raise specific exception when smallest denomination of a currency is not defined
Add tests for rounding to nearest possible cash value
Extend tests for rounding to nearest possible cash value to include negative amounts of money
Use configured rounding mode for rounding to nearest cash value
Merge pull request #433 from tweymuth/master

Add method to round to nearest possible amount of cash (aka Swedish rounding)