Story and Task Estimation and Actuals

Hi, We have customized the story workflow as per our need and we will add tasks (child) under stories (parent). The tasks will be assigned to the different people and it is tracked. One requirement from the Business Partner is to roll up the estimation and actual efforts entered to the task to the STORY level. Since they own the story, they need need to find out how much time was used to complete a story.
When I add tasks under a story, the numbers for Estimation and Actuals are not getting rolled up. Is there a way to configure them without writing plugins ? Thanks.