Optimize on Cost/Number of shipments" flag at scheduling rule level.

As per product logic system first considers the cost of each option and then moves on to the number of shipments.

For cost to be considered, select the Optimization Criterion at Scheduling rules level to be Optimize on Cost/Number of shipments and then check the 'Use Landed Cost' flag at the DOM-Cross Application-Order Promising-Sourcing and Scheduling-Landed cost. In this screen select the Use item cost, use Handling cost, and convert node priority into cost flag. For shipping cost, user can make use of the YDMGetTransportationCostUE or make use of the transportation cost in the landed cost screen.
As per the design, cost comes in to picture only when the Landing cost enabled flag is checked.
Otherwise number of shipments is considered as the base-mark for cost optimization.
In the presence of landed cost, first the possible options are obtained based on the sourcing rules. Then optimization comes into picture (scheduling rules).
Here, when cost is the optimization criterion; all the configured costs are considered, that is the handling cost and the item cost at one go.
In this same step, there is an internal call to the determineRouting API which checks for the carrier.
Now, if the costs are handled through the getTransportationCost UE, it gets invoked, else the transportation cost is calculated using the transportation cost configured at the landed cost level (based on distance covered).

Using this process the entire cost is calculated and the best cost effective option is chosen.
Please note that if all the options have the same cost, then the node having highest priority will become the ShipNode and if all options are form the same node, then the earliest delivery date option is selected.
If all the parameters such as cost, priority, date for all the options are the same, then all these options are equally valid options.As such, any node will be selected at random for the order as there is no other criteria to differentiate between them.