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 $231.62   13.115%   $261.997   $262.00   $262.00   $262.00  
  Purchase #2 $68.46   7.152%   $73.3563   $73.36   $73.35   $73.40  
  Purchase #3 $54.59   7.611%   $58.7448   $58.74   $58.75   $58.70  
  Purchase #4 $249.89   10.102%   $275.1339   $275.13   $275.15   $275.10  
  Purchase #5 $248.35   11.602%   $277.1636   $277.16   $277.15   $277.20  
  Purchase #6 $147.41   10.864%   $163.4246   $163.42   $163.40   $163.40  
  Purchase #7 $237.69   4.118%   $247.4781   $247.48   $247.50   $247.50  
  7 purchase totals = $1,238.01       $1,357.2983   $1,357.29   $1,357.30   $1,357.30