Data Grid Pre-Save Accounts aggregation using Groovy?

Summary

Trying to create a Groovy business rule to prevent the save of a data form if Total Revenue does not match Total Expenses

Content

The rule I have can compare the exact intersections, but any new data entered into the form does not roll up into Total Revenue / Expense unless the form is saved. So I am essentially comparing old data. Short of adding up the data in every cell of the "data grid", is there any way I can get the data form to "calculate" before saving? I am trying to avoid summing up the cells and use outline consolidation instead to make the numbers accurate.