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   6.454%   $262.2707   $262.27   $262.25   $262.30  
  Purchase #2 $185.74   9.478%   $203.3444   $203.34   $203.35   $203.30  
  Purchase #3 $122.64   8.380%   $132.9172   $132.92   $132.90   $132.90  
  Purchase #4 $82.48   7.170%   $88.3938   $88.39   $88.40   $88.40  
  Purchase #5 $209.53   6.825%   $223.8304   $223.83   $223.85   $223.80  
  Purchase #6 $115.99   3.301%   $119.8188   $119.82   $119.80   $119.80  
  Purchase #7 $237.81   10.121%   $261.8788   $261.88   $261.90   $261.90  
  7 purchase totals = $1,200.56       $1,292.4541   $1,292.45   $1,292.45   $1,292.40