Ask HN: What taxation software do you normally use for ecomm?

At my job we are currently starting up a new ecomm project and I am really curious what taxation software you guys normal use. We need to be able to look up various tax rates for products and services by zip code.

We are a rails shop and I would love to find something like braintree for taxation but that doesn't appear to be out there. We have looked at billsoft and vertex, but they don't seem to promote a nice api.

Strikeiron and taxcloud appear to be options, but I question how scalable they are. Has anyone used them?

Finally, thanks in advance for your great advice.