The cost of an inventoried item is used for the following purposes:
Calculating sales tax versus use tax
Calculating margins
Calculating the total value of inventory in stock
Other reporting purposes
The IDI platform lets you track the cost of inventory per store, SKU and, if the inventory is serialized, by serial number.
For non-serialized items, the cost is determined by the average cost of the items in inventory. This is displayed in the Inventory Cost History window.

See Viewing Cost History
For serialized items, the actual cost of the single item is tracked directly in the serialized inventory record. This is displayed in the Inventory Search Results for Serial Number Detail window.

See Viewing Serialized Detail