Thank you for joining the thread, @amit15.

Yes, you can add tax for each line item. Beforehand, you’ll have to set up your sales tax in QuickBooks Online (QBO). Learn how to set up your Sales tax by checking out this article: Set up your sales tax in QuickBooks Online

After that, your invoices, sales receipts, estimates, and credit memos will all include a sales tax section. Apply sales tax by doing the following when in any of these windows:

1. Add your products and services in the form.
2. Check the box next to Tax for each taxable item in the Tax column.
3. Click in any white space to update the sales form. At the bottom right, select the appropriate sales tax.
    

You have the option to opt-out of collecting sales tax from clients who are tax-exempt (such as companies, non-profits, or charities, to name a few). By default, every client is "taxable." 

Furthermore, I added this article to learn more when applying sales tax to your transactions in QBO: Apply sales tax rates to transactions and sales forms in QuickBooks Online

Let me know if you need further assistance with taxes. The Community always has your back. Stay safe!