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 $51.86   13.204%   $58.7076   $58.71   $58.70   $58.70  
  Purchase #2 $183.59   5.656%   $193.9739   $193.97   $193.95   $194.00  
  Purchase #3 $34.63   11.513%   $38.617   $38.62   $38.60   $38.60  
  Purchase #4 $237.25   4.200%   $247.2145   $247.21   $247.20   $247.20  
  Purchase #5 $122.43   11.543%   $136.5621   $136.56   $136.55   $136.60  
  Purchase #6 $236.47   12.650%   $266.3835   $266.38   $266.40   $266.40  
  Purchase #7 $207.44   13.144%   $234.7059   $234.71   $234.70   $234.70  
  7 purchase totals = $1,073.67       $1,176.1645   $1,176.16   $1,176.10   $1,176.20