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 $248.93   7.351%   $267.2288   $267.23   $267.25   $267.20  
  Purchase #2 $42.36   10.716%   $46.8993   $46.90   $46.90   $46.90  
  Purchase #3 $77.63   6.216%   $82.4555   $82.46   $82.45   $82.50  
  Purchase #4 $58.71   3.234%   $60.6087   $60.61   $60.60   $60.60  
  Purchase #5 $52.85   10.667%   $58.4875   $58.49   $58.50   $58.50  
  Purchase #6 $250.27   3.734%   $259.6151   $259.62   $259.60   $259.60  
  Purchase #7 $248.57   5.395%   $261.9804   $261.98   $262.00   $262.00  
  7 purchase totals = $979.32       $1,037.2753   $1,037.29   $1,037.30   $1,037.30