Cost of Goods Sold (COGS) Calculation: A retailer purchased inventory for $100,000, incurred $20,000 in transportation costs, and paid $5,000 in import duties. However, the retailer also received a volume discount of 10% on the inventory purchase. Calculate the cost of goods sold (COGS) for the retailer, considering the various cost components and adjustments. Additionally, discuss how COGS affects the company's gross profit margin and overall profitability.