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 $241.88   8.145%   $261.5811   $261.58   $261.60   $261.60  
  Purchase #2 $111.66   9.584%   $122.3615   $122.36   $122.35   $122.40  
  Purchase #3 $26.75   10.141%   $29.4627   $29.46   $29.45   $29.50  
  Purchase #4 $143.71   13.727%   $163.4371   $163.44   $163.45   $163.40  
  Purchase #5 $196.65   13.523%   $223.243   $223.24   $223.25   $223.20  
  Purchase #6 $78.38   11.528%   $87.4156   $87.42   $87.40   $87.40  
  Purchase #7 $150.74   8.384%   $163.378   $163.38   $163.40   $163.40  
  7 purchase totals = $949.77       $1,050.8790   $1,050.88   $1,050.90   $1,050.90