We do not recommend comparing Dashboard totals to a Report totals. Dashboard was designed to give users a real-time snapshot of their organization's progress.  it was not designed as as reporting tool to use in place of a report from the Reports module   Due to the differences in flexibility and customization between Dashboards and Report, we do not recommended comparing totals.

If viewing certain Dashboard panels, like the Campaign Summary, Fund Summary or Appeal Summary the different columns calculate based on hard coded settings that cannot be modified.  See this article for more specifics on Amount Received, Variance and Total Committed are calculated.