In design view, bring up the Property sheet. Click on the text box for hourly rate. You should see on the property sheet a tab that says Event. You should have in your table fields to store annual salary, Fica %, and retirement %. You should have on your form three corresponding textboxes. Then on the AfterUpdate event of the hourly rate textbox, you would write the appropriate code.
And it's true you should not keep totals in tables because if someone changes something in the table the totals are not automatically updated. And it violates 3NF. But that's up to you.
Neil