"唔係1蚊幾毫問題"... No offense, but I think it is 1蚊幾毫. It is your own fault that you are buying 5, the sales lady did nothing wrong to remind you about "buying 6".
I think she might have an attitude problem that day, but I've been there a lot of times and they've always been really nice...
NO, I never been charged for HST/GST when I buy plain bread,
crusty roll, french bread, Multi-grain bread.
On the other hand, cocktail buns, Cha Siu Bao are classified as pastries
which is subjected to GST since 1991