Why pzmap says my poles have an imaginary part when they shouldn't have it?

I have the following transfer function:

48600/((s+90)^2 * (s+15) * (s+0.4))

and my poles should all have no imaginary part... Why I'm getting for my poles of real part's value of -90 an imaginary part different from zero that is what it should have? I got the fact that is very little and it can be considered zero, but why this function says it even exists?

Answer 1

[Walter Roberson]

Round off error.

http://matlab.wikia.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_.28or_similar.29_not_equal_to_zero.3F