Error approximation for an alternating series

So for this question, I first had to find the Maclaurin polynomial of $f(x)=5\cos(0.2x)$ which I found to be $5[1-\frac{(0.2x^2)}{2}+\frac{(0.2x^4)}{4!}]$, and the second part asks:
"Find the largest integer k such that for all x for which |x|<1 the Taylor polynomial $T_{5}(x)$ approximates f(x) with error less than $10^{-k}$.

I really don't know how to go about doing this. Do you have any suggestions?