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 $117.57   7.298%   $126.1503   $126.15   $126.15   $126.20  
  Purchase #2 $187.70   6.586%   $200.0619   $200.06   $200.05   $200.10  
  Purchase #3 $244.25   7.177%   $261.7798   $261.78   $261.80   $261.80  
  Purchase #4 $157.42   4.409%   $164.3606   $164.36   $164.35   $164.40  
  Purchase #5 $160.97   7.808%   $173.5385   $173.54   $173.55   $173.50  
  Purchase #6 $10.49   7.111%   $11.2359   $11.24   $11.25   $11.20  
  Purchase #7 $67.92   12.720%   $76.5594   $76.56   $76.55   $76.60  
  7 purchase totals = $946.32       $1,013.6864   $1,013.69   $1,013.70   $1,013.80