Could you please collect support data to let me reproduce it locally? Enable Track Support Data option in add-on configuration, then reload report and click Download Support Zip button, and send it to firstname.lastname@example.org.
I am afraid you have a bug then. Each individual value in Total column is rounded to "Maximum Fraction Digits " but the Grand Total (bottom right value) does not represent the sum of rounded Totals, but is getting rounded AFTER the grand total is calculated. This problem was highlighted by excel export - if you sum up each individual rounded total, it will not match the grand total.