Do I need to enter all sales from Robinhood 1099B or can I enter just the Grand Total?

You can enter the Sales Total summaries from your 1099-B. When you get to the section to enter your sales, you can import your 1099-B and TurboTax will import all the data into your tax return. Or you can enter the sales totals manually. If you prefer to enter manually, make sure to have your 1099-B available and select "Enter a different way" when you get to the screen shown below:

Answer the question on the next few screens and you will get to the screen to select how you want to enter your sales. Make sure "Sales section totals" is selected and continue entering the info from your 1099-B.