Although we don't believe in timing the market or panicking over daily movements, we do like to keep an eye on market changes -- just in case they're material to our investing thesis.

Retail stocks can be a lot like the merchandise and the sales of the companies they represent -- in constant fluctuation. In this column I like to point out a few notable daily moves from the big retail stocks and help investors figure out whether they should buy, sell, or hold. Today's movers and shakers: Starbucks (NASDAQ:SBUX), Groupon (NASDAQ:GRPN), and J.C. Penney (NYSE:JCP).

Shares of coffee king Starbucks fell 2.77% today on little direct news. However, investors may be growing concerned about the company's costs, as Brazil's unusually dry and hot growing season is contributing to the rising price of beans. What sold in November for $1 a pound is now $1.50 and could, some say, jump as high as $2. If prices stay high, short-term profits will falter until Starbucks adjusts its prices, but higher prices could hurt business in the long term. Investors need to keep an eye on the developments here.

After falling more than 20% last week, shares of Groupon gained 8.1% -- again on little direct news. Trading volume was massive -- 65.7 million shares, compared with the typical 19.5 million -- which, combined with last week's price drop, probably means a large institutional investor perceives a bargain and is building a position. We won't know right away if that's the case, but today's jump could attract other investors to this struggling online retail platform.

Finally, J.C. Penney is set to report quarterly earnings tomorrow, and with management insisting that business is turning around, investors voted shares up 7.65% this afternoon. Analysts are estimating revenue of $3.86 billion, just off the $3.88 billion figure from a year ago, and an earnings loss of $0.82 per share, which would actually be a vast improvement over last year's $1.95-per-share loss. If J.C. Penney hits or exceeds the estimates, today's jump will be justified. If the retailer disappoints, we could really see the bottom fall out. I'd need to see quite a few positive earnings reports before I'd ever say that the reward would outweigh the risk with this faltering retailer.  

Matt Thalman owns shares of Starbucks. The Motley Fool recommends and owns shares of Starbucks. Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.