My question is:
Every built in operators (+-*/) and math functions (like: sin, cos, sqrt, ...)
acts on floating point numbers a way like the result is rounded to the nearest representable floating point number?
The numbers are not rounded -- excess digits that won't fit in the size of the float or double are just dropped (truncated). Thus if the actual value is 1.236 but only three digits fit in the variable than the variable's value will be 1.23.
Here is a more thorough and accurate description of the problem.