3E+07 means 3 followed by 7 zeros and is spoken as "three times ten to the power of seven".
If your totals are always whole numbers you can specify the formatting of the answer like this
Code:
MsgBox Format(Selection.Calculate,"#,##0")
or show two decimal places like this
Code:
MsgBox Format(Selection.Calculate,"#,##0.00")
Hint: You can experiment with number formatting in Excel to work out number formatting strings to use in this VBA.