Hi Courtz,
Welcome to WAB.
I'm assuming you're American with you reference to a 10 cent piece?
If you are in the US then I might not be able to help you much as I mainly deal with spiders that are around me (UK and Europe)
I don't suppose there is any chance of a photo? there are an awful lot of spider species out there and
"small black spider that looks like it has a hard body, fangs and a white patch on its back" doesn't really give us a lot of information.
Anyway, as a rough guess go look at
Steatoda sp a member of the
Theridiidea family.