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 $24.62   8.630%   $26.7447   $26.74   $26.75   $26.70  
  Purchase #2 $165.70   10.102%   $182.439   $182.44   $182.45   $182.40  
  Purchase #3 $74.89   4.844%   $78.5177   $78.52   $78.50   $78.50  
  Purchase #4 $234.57   10.771%   $259.8355   $259.84   $259.85   $259.80  
  Purchase #5 $226.73   5.300%   $238.7467   $238.75   $238.75   $238.70  
  Purchase #6 $31.85   9.739%   $34.9519   $34.95   $34.95   $35.00  
  Purchase #7 $249.56   4.504%   $260.8002   $260.80   $260.80   $260.80  
  7 purchase totals = $1,007.92       $1,082.0357   $1,082.04   $1,082.05   $1,081.90