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 $241.43   8.170%   $261.1548   $261.15   $261.15   $261.20  
  Purchase #2 $207.58   12.273%   $233.0563   $233.06   $233.05   $233.10  
  Purchase #3 $42.71   3.165%   $44.0618   $44.06   $44.05   $44.10  
  Purchase #4 $91.95   5.228%   $96.7571   $96.76   $96.75   $96.80  
  Purchase #5 $47.84   5.779%   $50.6047   $50.60   $50.60   $50.60  
  Purchase #6 $48.94   8.202%   $52.9541   $52.95   $52.95   $53.00  
  Purchase #7 $151.91   3.784%   $157.6583   $157.66   $157.65   $157.70  
  7 purchase totals = $832.36       $896.2471   $896.24   $896.20   $896.50