The online documentation promises this
probe to-money 123
$123.00
http://www.rebol.com/r3/docs/datatypes/money.html
I get this
probe to-money 123
$123
The documentation you see is a copy of R2 documentation. It still does not reflect the current state in R3.
In R3 you can have both $123 as well as $123.00, have you tried?
This looks like a more accurate documentation: