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 $215.46   11.270%   $239.7423   $239.74   $239.75   $239.70  
  Purchase #2 $240.33   12.185%   $269.6142   $269.61   $269.60   $269.60  
  Purchase #3 $122.91   8.337%   $133.157   $133.16   $133.15   $133.20  
  Purchase #4 $84.76   13.728%   $96.3959   $96.40   $96.40   $96.40  
  Purchase #5 $159.32   3.138%   $164.3195   $164.32   $164.30   $164.30  
  Purchase #6 $172.81   10.246%   $190.5161   $190.52   $190.50   $190.50  
  Purchase #7 $26.88   11.267%   $29.9086   $29.91   $29.90   $29.90  
  7 purchase totals = $1,022.47       $1,123.6536   $1,123.66   $1,123.60   $1,123.60