Not less than 15 units or 15% of the total number of units shall be affordable to very-low-, low- and moderate-income households for rental units and not less than 20 units or 20% of any for sale units shall be affordable to very-low-, low- and moderate-income households. Any computation resulting in a fraction of less than 0.5 shall be rounded down; any computation resulting in a fraction of more than or equal to 0.5 shall be rounded up.