I just researched this for a client. He does not want QuickBooks and wanted something 100% web based.
We set him up with a Shopify cart, Vend POS system and Xero accounting. All 3 are web based and integrate with each other.
Not really sure if something like this suitable for firearm sales or if it even meets whatever requirements there are. The client I have researched this for manufactures electronic equipment for DNA testing.