According to the Texas Court at Appeals blog, the CCA will take up the issue of whether forgery of a "commercial instrument" includes a store receipt.

The Sixth Court of Appeals (Texarkana) didn't think so, limiting the definition to instruments that affect a legal relationship or convey some sort of future benefit, and excluding a store receipt because it simply memorializes a transaction that has already occurred. Here's the court of appeals opinion: Allen Ray Shipp v. State.