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 $19.89   4.387%   $20.7626   $20.76   $20.75   $20.80  
  Purchase #2 $151.70   3.656%   $157.2462   $157.25   $157.25   $157.20  
  Purchase #3 $12.48   7.483%   $13.4139   $13.41   $13.40   $13.40  
  Purchase #4 $209.26   6.528%   $222.9205   $222.92   $222.90   $222.90  
  Purchase #5 $21.91   6.538%   $23.3425   $23.34   $23.35   $23.30  
  Purchase #6 $47.49   13.318%   $53.8147   $53.81   $53.80   $53.80  
  Purchase #7 $74.54   8.629%   $80.9721   $80.97   $80.95   $81.00  
  7 purchase totals = $537.27       $572.4725   $572.46   $572.40   $572.40