Setting precision of a result for the next calculation

Sorry for my easy question.

I would like to learn how I could change the precision of a value to use it for the next calculation ?

Lets say, a=9.96329×10^-13, in fact this value is so small and can be taken as zero. However, I don’t know how to impose Mathematica to take it zero by setting its precision.

I need to multiply the value of a with the b value which is equal to 10^15 and if I can’t arrange the precision of the a,the multiplication will give the result of 10^12 which in reality I want it to be zero.

Could you help me about this issue ?

Best Regards,