While you certainly can use nylon and pull it tight, it does stretch. In most cases stretch is ok, but for instance winter camping snow load may drop your tarp onto you if tied up with nylon, in which case spectra, dyneema, or the relatively inexpensive pre stretched poly rope sold in marine supply stores would be better. Check on ebay. Personally I use 4,000 pound test spectra rope because its easier to work with than string, but still extremely light, amsteel would be overkill even beyond spectra rope.
Jim