Question: Precision dropping?

I have a function: s^5+3.236067976*s^4+(1.*10^(-10)*I)*s^4+5.236067975*s^3+(7.*10^(-10)*I)*s^3-(3.*10^(-10)*I)*s+5.236067975*s^2+3.236067977*s+1.000000000 and I want to drop those terms in s^4, s^3 and s^2 with magnitude less than for example 10^8. I want those imaginary terms gone so I can see my transfer function with only real coefficients. I don't even know what this would be called... so I wasn't able to search for it.
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