In scientific work you need to use significant figures.

A That is 0.1345 is 4 sig fig or 1.345e-1.
B But 0.01345 is also 4 sig figures or 1.345e-2.

My problem is i need to truncate to 3 sig figures and not to 3 decimal
places. How can I round and make the numbers look like:

A 1.35e-1
B 1.35e-2

Thanx for the help