prevent admin (my developer) from accessing woocommerce sales data

I don’t think this is possible. As an admin user he will be able to go anywhere in your dashboard. If you manage to find a plugin to prevent access, he will be able to disable it if he is so minded. Also its likely your developer will have and need access to your hosting account, allowing full access to the database and therefore to the data therein.

What you could do is have him set up a separate install in different hosting to build and alter the site. When its working and ready, deactivate the live site, backup and delete your shop data, ask him to update the live site, change passwords including hosting, then restore your shop data.

But the first time you need a bug fix, you will need to let him back in!