April was a tough month for retailing giant Costco (NASDAQ:COST). After achieving March highs while customers stocked up for the coronavirus pandemic, Costco saw April sales decrease for the first time in 10 years as people stayed home and the company had to close some departments in accordance with government regulations. However, May sales bounced back big, with a 7.5% increase in sales year over year to $12.55 billion.

E-commerce came through

Costco, unlike most publicly traded companies, releases monthly earnings reports. The May earnings report included the four weeks ended May 31. Although it was solid all around, Costco saw a 105% increase in e-commerce, which is crucial for the company as it competes with the likes of Walmart and Target, who are both succeeding in that area.

Couple putting a box into their car.

Image source: Getty Images.

In the company's third quarter, which ended May 10, e-commerce comps increased 64.5%, which was lower than Walmart's 74% increase and Target's 141% increase during a similar time period.

But customers are still coming in

U.S. comps increased 5.5% and total comps excluding gas price declines and currency exchange was 9.7%. In the third quarter, e-commerce sales were only 8% of total sales, so while the increase bodes well for Costco's ability to convert customers to digital patrons, the retailer is still maximizing its in-store business. 

Costco stock has stayed fairly steady through the pandemic and is up 4.3% year to date. Shares rose in trading based on the May results.

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