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 $214.46   11.766%   $239.6934   $239.69   $239.70   $239.70  
  Purchase #2 $199.97   11.374%   $222.7146   $222.71   $222.70   $222.70  
  Purchase #3 $178.97   9.135%   $195.3189   $195.32   $195.30   $195.30  
  Purchase #4 $104.73   8.240%   $113.3598   $113.36   $113.35   $113.40  
  Purchase #5 $248.65   4.375%   $259.5284   $259.53   $259.55   $259.50  
  Purchase #6 $250.93   8.239%   $271.6041   $271.60   $271.60   $271.60  
  Purchase #7 $152.64   11.248%   $169.8089   $169.81   $169.80   $169.80  
  7 purchase totals = $1,350.35       $1,472.0281   $1,472.02   $1,472.00   $1,472.00