Allow each U.S. State to use its own money rounding

Right now there's one utils function for rounding money, but I _think_ each State chooses its own way to round money. It's possible it's not even that simple - it may be per State per program or per circumstance - but it might be necessary to abstract the operation and we can start by doing it for the States.

Start by locating the existing utility function for rounding money. Research whether rounding rules vary by state, program, or circumstance before deciding on the scope. Done should mean the requirements are confirmed and the rounding operation can support the required state-specific rules with corresponding tests.

Written by the indexing model from the issue text.