Yeah, it's a rounding thing. I'm guessing your site is so lightweight that the cost ends up being negligible. You should be able to click through from the result page to a fully detailed report from webpagetest.org.

It seems to work fine at the moment: https://i.imgur.com/WSCMaxC.png

I got the same result, but my site weighs 0.01MB apparently (it's actually lower at 6kB according to webpagetest.org).

I think small sized sites weigh next to nothing. This is more intended for people with much bigger sites.

Looks like your site just costs less than a cent everywhere. Rejoice!