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 $72.92   13.305%   $82.622   $82.62   $82.60   $82.60  
  Purchase #2 $111.50   5.163%   $117.2567   $117.26   $117.25   $117.30  
  Purchase #3 $124.46   9.660%   $136.4828   $136.48   $136.50   $136.50  
  Purchase #4 $21.93   4.635%   $22.9465   $22.95   $22.95   $22.90  
  Purchase #5 $100.28   5.432%   $105.7272   $105.73   $105.75   $105.70  
  Purchase #6 $238.41   5.115%   $250.6047   $250.60   $250.60   $250.60  
  Purchase #7 $6.58   8.256%   $7.1232   $7.12   $7.10   $7.10  
  7 purchase totals = $676.08       $722.7631   $722.76   $722.75   $722.70