Round() should support negative decimal places

Support rounding to a whole power of ten: Maths.Round() and Double.Round() should accept negative decimal places so a value can be rounded to the nearest 10, 100, 1,000, and so on.

Rounding to the nearest 100 or 1,000 is a recurring need, for example when presenting amounts at a preferred magnitude for business trade lines. Today it requires a Divide/Round/Multiply workaround such as Maths.Round(value / 100) * 100. This change makes Maths.Round(value, -2) round directly to the nearest 100 in one native call, preserving the existing ties-to-even (banker's) rounding semantics.