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 $60.70   9.278%   $66.3317   $66.33   $66.35   $66.30  
  Purchase #2 $235.61   3.854%   $244.6904   $244.69   $244.70   $244.70  
  Purchase #3 $14.56   6.179%   $15.4597   $15.46   $15.45   $15.50  
  Purchase #4 $32.34   13.578%   $36.7311   $36.73   $36.75   $36.70  
  Purchase #5 $20.47   3.826%   $21.2532   $21.25   $21.25   $21.30  
  Purchase #6 $175.42   9.491%   $192.0691   $192.07   $192.05   $192.10  
  Purchase #7 $155.33   8.105%   $167.9195   $167.92   $167.90   $167.90  
  7 purchase totals = $694.43       $744.4547   $744.45   $744.45   $744.50