I am not sure of the quantity of chewing tobacco one can bring into the country.
I know my wife was caught by customs for carrying 2 cartons of cigarettes and she forgot that she had them in the carry on luggage so she inadverently ticked the "green".
She was fined S$800 + gst. The reaon for the penalty was that (i) she did not declare and (ii) she was only allowed to carry one carton into the country.
Better check the rules and follow them cos the fines are very expensive. I believe there is a web site for Singapore customs.... anyone know it on the top of their heads? (or try doing a search on the internet).