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 $237.81   3.735%   $246.6922   $246.69   $246.70   $246.70  
  Purchase #2 $128.44   9.834%   $141.0708   $141.07   $141.05   $141.10  
  Purchase #3 $207.40   8.451%   $224.9274   $224.93   $224.95   $224.90  
  Purchase #4 $239.98   12.340%   $269.5935   $269.59   $269.60   $269.60  
  Purchase #5 $111.30   7.601%   $119.7599   $119.76   $119.75   $119.80  
  Purchase #6 $237.94   3.637%   $246.5939   $246.59   $246.60   $246.60  
  Purchase #7 $196.52   12.585%   $221.252   $221.25   $221.25   $221.30  
  7 purchase totals = $1,359.39       $1,469.8897   $1,469.88   $1,469.90   $1,470.00