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 $112.82   12.154%   $126.5321   $126.53   $126.55   $126.50  
  Purchase #2 $111.74   3.202%   $115.3179   $115.32   $115.30   $115.30  
  Purchase #3 $70.86   10.429%   $78.25   $78.25   $78.25   $78.30  
  Purchase #4 $8.63   10.301%   $9.519   $9.52   $9.50   $9.50  
  Purchase #5 $241.94   12.122%   $271.268   $271.27   $271.25   $271.30  
  Purchase #6 $68.93   9.637%   $75.5728   $75.57   $75.55   $75.60  
  Purchase #7 $64.47   4.603%   $67.4376   $67.44   $67.45   $67.40  
  7 purchase totals = $679.39       $743.8974   $743.90   $743.85   $743.90