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 $239.52   10.705%   $265.1606   $265.16   $265.15   $265.20  
  Purchase #2 $178.83   9.171%   $195.2305   $195.23   $195.25   $195.20  
  Purchase #3 $101.39   4.814%   $106.2709   $106.27   $106.25   $106.30  
  Purchase #4 $107.95   9.633%   $118.3488   $118.35   $118.35   $118.30  
  Purchase #5 $157.40   10.438%   $173.8294   $173.83   $173.85   $173.80  
  Purchase #6 $237.38   10.128%   $261.4218   $261.42   $261.40   $261.40  
  Purchase #7 $217.57   13.175%   $246.2348   $246.23   $246.25   $246.20  
  7 purchase totals = $1,240.04       $1,366.4968   $1,366.49   $1,366.50   $1,366.40