The problem isn't 10 cigars a year, the problem - as others have stated - is the chances of becoming "hooked" and smoking more. Our nephew started smoking, socially, when he was out with friends. Just a few to "fit in". He's now a full time smoker. Not in excess - but a few a day, every day. He'll quit one day, I'm sure.
Smoking even 10 cigars increases your risk of disease. But increased risk doesn't mean you get sick. It's all probabilities (just like gambling, eh?). So - no body can tell you whether it's harmful or not. You Probably won't get sick smoking 10 cigars. But that probability is every so slightly smaller, and probably not measurable - as has also been pointed out.
On the plus side, you probably more at risk just being in the smoking section of a casino. All of that 2nd hand smoke is in fact ending up in your lungs, and it's as if you are smoking cigarettes even if you aren't actually smoking your cigar.
Also, you are increasing your odds of risk just driving to the casino, eating those BBQ chips, and drinking that rum & coke.
Life is too short to worry about how bad (or not....) all of these things are....
Besides, you will live longer if you have funny growing up stories to tell when you are 60, like the time you had jump out of the casino window into the fountain to save your skin when your cigar burned a hole in the gang-boss' best tux. If you can laugh for 20 years about that story, you will live longer than the 10 cigars took away. Laughing is the best thing for your health.