depends on what they work on, business applications in large organizations we tend to direct programmers through reams of project documentation, from top level to familiarize them with what the overall direction is to technical documents which specify exactly the formulas to be used at all levels of calculation. These formula and related specification does include the number of decimals to use within calculation, rounding, and resulting decimal precision.

yeah its nice if they understand it all but programming isn't all shoot from the hip, many work in very structured environments which is more true when projects can have more than a dozen programmers on just one machine. Throw in three or more touch points and I am more concerned you follow the technical than branch out with your own ideas