It depends on what you call "start with a clean slate".
If it means getting rid of all configuration settings, products, orders, customers (not Joomla users), then deleting any #__hikashop_ tables before re-install is the right thing to do. Take a look at the table names, they do speak for themselves.
If you also want to get rid of view and/or CSS and/or language customizations and/or product images and thumbnails, you best delete related files, too.
Some menu items and modules may also remain in the system and might require extra effort, if you want to delete them completely before re-install.
I guess it goes without saying that a full, restorable backup of your site including database is highly recommended before deleting anything, even if you are about to reinstall an extension.