No. MATLAB is not making a rounding error, and will certainly not do this only sometimes. But we really do not know exactly what you have done here, as you say it results in "some" errors. Either it gives an unexpected result or it does not. Please show what you actually did that gave you a result you did not expect.
You may be stuffing the result into an integer variable. Or, possibly you are doing a divide between vectors, and do not realize that you need to be using ./ and not / as the operator.
