Delaware does not have sales tax, so there’s no sales tax certificate since you wouldn’t be collecting sales tax.
However, your nexus and where you pay taxes primarily depends on your nexus (where you are physically doing business), not necessarily where your LLC is formed.
Example:
This means that if you have a warehouse in California, you’d need to collect sales tax based on the state of California rules.
I would recommend that you call the state’s sales tax or revenue department to ask about these questions, or ask your CPA if they are familiar with this topic.