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 $91.65   11.248%   $101.9588   $101.96   $101.95   $102.00  
  Purchase #2 $76.84   3.174%   $79.2789   $79.28   $79.30   $79.30  
  Purchase #3 $70.47   8.764%   $76.646   $76.65   $76.65   $76.60  
  Purchase #4 $140.61   5.429%   $148.2437   $148.24   $148.25   $148.20  
  Purchase #5 $30.45   5.174%   $32.0255   $32.03   $32.05   $32.00  
  Purchase #6 $226.87   4.280%   $236.58   $236.58   $236.60   $236.60  
  Purchase #7 $40.38   10.755%   $44.7229   $44.72   $44.70   $44.70  
  7 purchase totals = $677.27       $719.4558   $719.46   $719.50   $719.40