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 $41.68   12.664%   $46.9584   $46.96   $46.95   $47.00  
  Purchase #2 $31.42   12.208%   $35.2558   $35.26   $35.25   $35.30  
  Purchase #3 $127.41   4.158%   $132.7077   $132.71   $132.70   $132.70  
  Purchase #4 $247.41   6.258%   $262.8929   $262.89   $262.90   $262.90  
  Purchase #5 $201.88   7.731%   $217.4873   $217.49   $217.50   $217.50  
  Purchase #6 $127.27   8.751%   $138.4074   $138.41   $138.40   $138.40  
  Purchase #7 $83.39   10.856%   $92.4428   $92.44   $92.45   $92.40  
  7 purchase totals = $860.46       $926.1523   $926.16   $926.15   $926.20