Perpetual inventory using LIFO Beginning inventory, purchases, and sales data for DVD players are as follows: The business maintains a perpetual inventory system, costing by the last-in, first-out method. units with the HIGHER unit cost first in the Cost of Goods Sold Unit Cost column and LOWER unit cost first in the Inventory Unit Cost column. The business maintains a perpetual inventory system, costing by the last-in, first-out method. units with the HIGHER unit cost first in the Cost of Goods Sold Unit Cost column and LOWER unit cost first in the Inventory Unit Cost column