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 $246.37   6.248%   $261.7632   $261.76   $261.75   $261.80  
  Purchase #2 $106.38   6.787%   $113.6   $113.60   $113.60   $113.60  
  Purchase #3 $178.64   5.224%   $187.9722   $187.97   $187.95   $188.00  
  Purchase #4 $222.35   5.745%   $235.124   $235.12   $235.10   $235.10  
  Purchase #5 $79.34   4.217%   $82.6858   $82.69   $82.70   $82.70  
  Purchase #6 $42.78   9.512%   $46.8492   $46.85   $46.85   $46.80  
  Purchase #7 $6.76   3.296%   $6.9828   $6.98   $7.00   $7.00  
  7 purchase totals = $882.62       $934.9772   $934.97   $934.95   $935.00