Using Excel to create calculation sheets with a 5mm grid
Solution 1:
I am able to get a 5.01 mm by 5.01 mm grid by adjusting the print scaling settings.
Under Page Setup | Scaling, change the value to 10%. Then adjust the row height and the column width to 5 mm and Excel will round it to 5.01 mm.
Keep in mind that a font size of 60 points at 10% scaling will print at 6 points. A 3-digit number of 6-point Calibri will display in a cell with width 5.01 mm.