If you set a Sales UOM, the given price is only available for this UOM. So if dozen is set with rounding to 1.00, this price is used for 1,2,3 dozen of given product only, but not for e.g. 1.5 dozen.
Please take into account to have a fallback Price without sales UOM. Otherwise the sales price of product is used for all price computation with deviating UOM.