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 $244.89   3.611%   $253.733   $253.73   $253.75   $253.70  
  Purchase #2 $237.90   5.352%   $250.6324   $250.63   $250.65   $250.60  
  Purchase #3 $76.94   10.403%   $84.9441   $84.94   $84.95   $84.90  
  Purchase #4 $32.91   11.496%   $36.6933   $36.69   $36.70   $36.70  
  Purchase #5 $55.37   11.738%   $61.8693   $61.87   $61.85   $61.90  
  Purchase #6 $184.37   6.190%   $195.7825   $195.78   $195.80   $195.80  
  Purchase #7 $35.69   12.678%   $40.2148   $40.21   $40.20   $40.20  
  7 purchase totals = $868.07       $923.8694   $923.85   $923.90   $923.80