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 $238.56   9.639%   $261.5548   $261.55   $261.55   $261.60  
  Purchase #2 $208.39   13.714%   $236.9686   $236.97   $236.95   $237.00  
  Purchase #3 $125.71   4.866%   $131.827   $131.83   $131.85   $131.80  
  Purchase #4 $176.92   10.723%   $195.8911   $195.89   $195.90   $195.90  
  Purchase #5 $231.29   9.167%   $252.4924   $252.49   $252.50   $252.50  
  Purchase #6 $162.69   11.715%   $181.7491   $181.75   $181.75   $181.70  
  Purchase #7 $15.46   7.516%   $16.622   $16.62   $16.60   $16.60  
  7 purchase totals = $1,159.02       $1,277.1050   $1,277.10   $1,277.10   $1,277.10