Just shafting the rewards to round down the fractional bars is not cool. Should give just give a different bar worth the same amount of the fractional portion or provide the same worth of the fractional portion of it in ore instead of bars.
Giving extra stuff doesn't really work, it has a base value (i.e. 5 bars), and multiplies that by the sum of your multipliers. And it just rounds it either down or to the nearest integer.
If you start giving extra items/bars/ore it will have to give random stuff, that you most likely dont need.
Maybe it should compensate by paying the partial bar at the current sell price.