Use of MAX function to get current Tax Code

Summary:

I need to tweak a repot which shows all the tax codes under one employee with dates against them, however I just need the current tax code that is applied.

Content (required):

I need to get the current tax code using the MAX function in an existing OTBI report which is listing all the tax codes one person has had on their records. I know that I'll need to use the latest date with the MAX function but what I would like to know is how I can use this to bring back the most recent tax code someone is on in a custom column within a report.