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 $48.93   7.526%   $52.6125   $52.61   $52.60   $52.60  
  Purchase #2 $104.97   9.870%   $115.3305   $115.33   $115.35   $115.30  
  Purchase #3 $52.34   5.610%   $55.2763   $55.28   $55.30   $55.30  
  Purchase #4 $235.93   3.441%   $244.0484   $244.05   $244.05   $244.00  
  Purchase #5 $122.55   13.699%   $139.3381   $139.34   $139.35   $139.30  
  Purchase #6 $35.93   7.257%   $38.5374   $38.54   $38.55   $38.50  
  Purchase #7 $247.74   5.334%   $260.9545   $260.95   $260.95   $261.00  
  7 purchase totals = $848.39       $906.0977   $906.10   $906.15   $906.00