Being able to widen the customization option for decimals is a good idea, Nahida.

Within QuickBooks Online (QBO), we cannot modify the format to display three decimal places. To explore different formatting options, navigate to your Account and Settings. The following steps will guide you:

1. Go to the Gear icon.
2. Select Account and Settings.
   
3. Click the Advanced tab.
4. Tap anywhere inside Other preferences.
5. Choose your preferred Number format in the drop-down arrow.
6. Hit Save, and then Done.
   

I can see the importance of having this option for your business. With that, I suggest sending feedback to our product developers so they can review it and might consider adding this in future updates. Please refer to the steps below:

1. Go to the Gear icon.
2. Under Profile, select Feedback.
3. Enter your suggestion.
4. Hit Next.
   

You can track your feature requests through our QuickBooks Online Feature Requests website.

Let me know in the comment below if you have other concerns or follow-up inquiries in QBO. I'm just around to help.