Hi there!

Running this puzzle is quite simple. Just executing the main file will do the trick. 
Actually, having the "xml-simple" gem will help. As in, will make it actually run. No additional
dependencies or gems were used. 

There are some test cases on the test/unit_test.rb file that could help to understand
better how everything goes and I've tried to comment as much as I could on how it works.

The first run of this problem used some dynamic programming tricks (like a to_usd_currency)
method and some reopening of the Float class to at a "round_half_even" method but ultimately,
most of that code appear to be more a show-off code than utilitarian so I reworked it to be more 
simpler. Also, I removed a lot of it to simplify it further. There is no better code than no code
at all.

Also, I changed my own function to use BigDecimal, and their support.