Employees and payroll
The OP wants to know how to get a 401k, calculated as a percentage, to include Tips in the calculation. You did not address the actual question with your answer.
To do this, make sure to list the Tip addition item before the 401k item, like this:
You can see here that the 10% 401-k deduction is calculating on $2000, including the Tips.
If you set up the employee record in this way, then it will be the default on new paychecks:
