I have always been told that dogs sneeze when they are happy, my sweet old Smooth Collie Murphy sneezes three times.
Jace, my Palomino has the heaves but never coughs any more, I give him a little "Cough Free" every day and it sure works, I would do a commercial for them!
I am an avid reader of Joe camp's books and when Jace and I did the Join-Up he came over to me and sniffed and licked me all over, I was patting and scratching him (he seemed almost hypnbotized by it) and then he sneezed 6 times, shook his head and went to his special Scratchy tree that I trimmed for him and scratched himself more.
When I pat him and scratch him and really make contact with him he sneezes then too. Not every day or every week. Is he just happy???