Grounds for wrongful termination lawsuit?

I got fired from my job at Wendy's in October of last year, and the reason they terminated me was labeled "Failure to follow proper cash procedures." What happened was I was signed onto the register and in charge of taking orders in the Drive - Thru. Around 11:30PM, we got an order and after I collected the customers money and finished what I needed to do in that area, I closed my drawer and went in the back to continue nightly cleaning. Keeping in mind, the order was not finished and the other two employees I was working with were still in the Drive-Thru by the window waiting to hand out the food. About 30 minutes after that car left, another one pulled up. I walked back up to my register to find it open and all my money was gone. Or in other words, I had been robbed. Apparently, my co-workers forgot to close and lock the window.. We called corporate, called the police and filed statements. The next day, I got suspended until further notice, and the day after was officially terminated. My district manager told me it was because I wasn't sure if "I" remembered to lock the window. Now, in my statement as well as 3 other people's statements, it said that I was not the last one by the window and therefor it was not my responsibility to lock it. So they labeled it Failure to follow proper cash procedures and I was terminated from my job that I had worked at for 2 and a half years... I know it's been some time since then, but I've been told I should file a lawsuit. Do I have grounds for Wrongful Termination? Any help would be appreciated!