Thanks for posting this concern in the Community space. I can provide information about rounding up FIT deductions in QBO payroll.
You may override the payroll amount for the FIT deduction manually on the Run Payroll page. Please see attached screenshots below.
This information should help you with rounding up FIT deduction. Let me know how things go once you've tried the steps. Feel free to comment below if you have other questions about QuickBooks. I'll be happy to answer.