Usually it is advisable to not save a separate record for anything that can be calculated with arithmetic. This is a general rule of database design because it introduces the potential for data inconsistency. It is advisable to instead only store the 5 columns and calculate the average value in the 6th column when displayed. That could be done in the database SELECT statement, or with PHP when displaying the page.
In the SELECT it might look like: SELECT *, ROUND((col1+col2+col3+col4+col5)/5, 2) AS colAverage FROM tableName