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 $234.69   11.510%   $261.7028   $261.70   $261.70   $261.70  
  Purchase #2 $54.66   4.786%   $57.276   $57.28   $57.30   $57.30  
  Purchase #3 $22.53   8.344%   $24.4099   $24.41   $24.40   $24.40  
  Purchase #4 $73.41   5.205%   $77.231   $77.23   $77.25   $77.20  
  Purchase #5 $240.86   10.845%   $266.9813   $266.98   $267.00   $267.00  
  Purchase #6 $155.87   10.509%   $172.2504   $172.25   $172.25   $172.30  
  Purchase #7 $214.92   8.867%   $233.977   $233.98   $234.00   $234.00  
  7 purchase totals = $996.94       $1,093.8284   $1,093.83   $1,093.90   $1,093.90