We tried TaxJar and Taxcloud. Taxcloud is 10.00/mo if i remember correctly. bottom line is that neither were ever 'correct' so we never filed a single return. now we are using Avalara. 250 transactions for 50/year is less $4.17/mo and 500 transactions for $95 is $7.91/mo
Remember with Avalara, only the sales in your state(s) you collect sales tax in go against your transaction count. So, if you have 500 sales this week but only 4 are in your sales tax state then you only use 4 of the 250 or 500 or however many transaction. That being said, even over 1500/year transactions; they ease to file the state tax is worth it.
we used to export our orders from CS-cart into a spreadsheet with several functions that calculated the tax. it's easy, but since you can't limit your order export to previous month then as time goes on you start dealing with massive files.
If cost is more of a concern, i'd probably try to make taxjar work over TaxCloud. We just coulnd't find anyone that was able to get an add-on working properly for us.
The biggest issue is differentiating the origin of shipping and the destination. The cart (MVE and cs-cart) both handle the case where origin is the merchant's location. But MVE shipping does not correctly account for vendor shipments and cs-cart doesn't correctly account for Supplier shipments.
Ie. an order contains 3 items from 2 vendors (or suppliers).
Vendor 1 is in NY and has 2 items
Vendor 2 is in Oregon with 1 item
And merchant is in California
Should be that tax should be collected on the items and shipping from Vendor 1 and not tax on items or shipping on Vendor 2 or the Merchant.
I'm not aware of the taxes in cs-cart being vendor specific (which they should be). I.e. each vendor should have their own tax tables setup and/or integration for each vendor to one of the tax rate services identified above.