按“其他”分组，其中贡献较小的组包含在“其他”字段中 - MySQL

I would like to GROUP BY an item in my table, which has an associated monetary value. This I can work out as a percentage, however there are often too many items in the list (too many to be useful, for example in a graph). Consequently, I would like to put those items that have a contribution to the total of less than say 5% into an 'Other' group. Any thoughts? I would like to GROUP BY an item in my table, w