New rules for skip counting

Me: Roshan, can you count by 10?
Roshan: Yes, I can, It is 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100.
Me: Wow! Taran, can you count by 3?
Taran: No, mummy, please ask me some tricky ones.
Me: Ok, can you count by 6?
Taran: It is 6, 12, 18, 24, 30 and 36.
Me: Excellent! Now, Rosh can you please count by 5?
Roshan: Ok. It is 5, 10, 12 ...
Taran, interjecting immediately and itching to give the answer: No, it is not 12. Please let me tell you what it is.
Roshan, vehemently sticking to his stand: No, it is 12.
Taran: No, it is not. Ok, please let me whisper the answer in your ears. It is 15.
Roshan: It is 12.
Me: Are you sure Rosh?
Roshan, aware that he made a mistake but not wanting to be outdone: Actually, they changed the skip counting from today. Till yesterday it was 5, 10 and 15 but from today it is 5, 10 and then 12.