Answer:
I am the tool, for inspiring many. Buy me in the store, for not much more than a penny. Don't overuse me, or my usefulness will go.
I have one eye. See near and far. I hold the moments you treasure and the things that make you weep.
Kills the bad ones and the sad ones. Tightens to fit, so one size fits.
At first, I am nothing. Add something to negate. Add again to oppose. Add again to find the time to draw. Add once more to find nobody at all.
I have three hundred cattle, with a single nose cord
Iām grown from darkness but shine with a pale light. Very round I am and always a lady's delight.