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 $101.47   12.523%   $114.1771   $114.18   $114.20   $114.20  
  Purchase #2 $30.38   4.427%   $31.7249   $31.72   $31.70   $31.70  
  Purchase #3 $76.61   3.417%   $79.2278   $79.23   $79.25   $79.20  
  Purchase #4 $96.52   5.490%   $101.8189   $101.82   $101.80   $101.80  
  Purchase #5 $210.92   12.482%   $237.247   $237.25   $237.25   $237.20  
  Purchase #6 $239.99   10.697%   $265.6617   $265.66   $265.65   $265.70  
  Purchase #7 $63.87   4.434%   $66.702   $66.70   $66.70   $66.70  
  7 purchase totals = $819.76       $896.5594   $896.56   $896.55   $896.50