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 $74.85   11.727%   $83.6277   $83.63   $83.65   $83.60  
  Purchase #2 $232.89   10.329%   $256.9452   $256.95   $256.95   $256.90  
  Purchase #3 $172.83   13.274%   $195.7715   $195.77   $195.75   $195.80  
  Purchase #4 $74.86   4.134%   $77.9547   $77.95   $77.95   $78.00  
  Purchase #5 $42.71   4.507%   $44.6349   $44.63   $44.65   $44.60  
  Purchase #6 $123.50   11.350%   $137.5173   $137.52   $137.50   $137.50  
  Purchase #7 $149.44   8.375%   $161.9556   $161.96   $161.95   $162.00  
  7 purchase totals = $871.08       $958.4069   $958.41   $958.40   $958.40