Here's one way to do it; this example is for SQL Server, you'll need to amend per your backend database SQL functions (e.g. it will be different for Informix, Oracle, etc.)
Create a Universe filter. In the WHERE condition use the following:
@Select(Your Date Object) between dateadd(d,-5,@Prompt('Date:','D',,mono, free)) and @Prompt('Date:','D',,mono, free)
The first part - @Select - you should select the date object you want to filter.
The next part - dateadd(d,-5,@Prompt('Date:','D',,mono, free)) - will prompt the user for a date and will subtract 5 days from it (for anything other than 5 days, amend the number. The 'd' represents days, this can be substituted with months and years - see the DATEADD link in the above post)
Finally, we use the same prompt without the Dateadd function - which returns the same date as above.
Therefore, when the report is run, the user is prompted for a date, and the query is filtered to return only dates between the five days before the prompted date, and the prompted date itself.
HTH
NMG