I don't think Benford's law applies here: it's about the first digit of numbers (that are distribute in a certain way), but in most cases the first digit of a price will be denominating dollars, not cents.
The change may be more than a dollar, so tens of cents is not necessarily the leading digit.
the amount of coin change is never more than a dollar.
The amount of coin change is the remainder left over after dividing the total change by a dollar. Thus although the total change may or may not obey Benford's Law, the coin change certainly doesn't.