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 $96.51   5.249%   $101.5758   $101.58   $101.60   $101.60  
  Purchase #2 $13.58   8.196%   $14.693   $14.69   $14.70   $14.70  
  Purchase #3 $192.65   8.455%   $208.9386   $208.94   $208.95   $208.90  
  Purchase #4 $229.36   4.271%   $239.156   $239.16   $239.15   $239.20  
  Purchase #5 $154.34   12.390%   $173.4627   $173.46   $173.45   $173.50  
  Purchase #6 $29.92   3.233%   $30.8873   $30.89   $30.90   $30.90  
  Purchase #7 $112.71   5.412%   $118.8099   $118.81   $118.80   $118.80  
  7 purchase totals = $829.07       $887.5233   $887.53   $887.55   $887.60