Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $95.49   11.733%   $106.6938   $106.69   $106.70   $106.70  
  Purchase #2 $40.94   9.274%   $44.7368   $44.74   $44.75   $44.70  
  Purchase #3 $57.38   11.848%   $64.1784   $64.18   $64.20   $64.20  
  Purchase #4 $236.46   11.204%   $262.953   $262.95   $262.95   $263.00  
  Purchase #5 $20.61   12.227%   $23.13   $23.13   $23.15   $23.10  
  Purchase #6 $127.88   13.157%   $144.7052   $144.71   $144.70   $144.70  
  Purchase #7 $234.42   10.854%   $259.8639   $259.86   $259.85   $259.90  
  7 purchase totals = $813.18       $906.2611   $906.26   $906.30   $906.30