Can I invoice customers from my LLC company in USA and add corresponding sales taxes, and also invoice EU people with VAT in € with the same company registered in Germany

Yes, you can, @Purruno.

You'll need to turn on the multi-currency feature so you can track invoices with sales taxes from the US and EU regions. Please note that you can't revert this once turned on. If you aren't sure, you can reach out to your accountant for proper guidance. 

Once ready, here's how to proceed:

1. Click the Gear icon ⚙️, and then select Account and Settings.
2. Choose Advanced.
3. Select Edit ✎ in the Currency section and choose your Home Currency.
4. Pick the Multicurrency checkbox and confirm that you understand that you can't undo this option.
5. Hit Save and close.
   
   
   

For more info, please check out this article: Turn on multi-currency.

Once turned on, all income and expense accounts will base on the home currency. To have an invoice with Eur (Euro) as the currency, you'll have to create a customer using that said currency. Here's how:

1. Go to the Sales menu, and then choose the Customers tab.
2. Tap the New Customer button.
3. On the Customer Information window, select the Payment and billing section.
4. Set the currency to Euro (€) under the This customer pays me with drop-down ▼.
5. Click Save when you're ready.
   
   

Once done, you can now create invoices with sales taxes using the said currencies. Just ensure to select the customer associated with it.

You'll want to customize your invoices to get the formats and info you need. Also, you can check the Sales Tax Liability report to keep track of all your sales tax info. For more insights, please review this resource: Run Sales tax Liability report.

You can count on me if you have more questions about managing your invoices. Take care and stay safe, @Purruno.