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 $55.65   13.105%   $62.9429   $62.94   $62.95   $62.90  
  Purchase #2 $140.28   7.802%   $151.2246   $151.22   $151.20   $151.20  
  Purchase #3 $166.32   4.398%   $173.6348   $173.63   $173.65   $173.60  
  Purchase #4 $114.47   13.403%   $129.8124   $129.81   $129.80   $129.80  
  Purchase #5 $193.76   12.418%   $217.8211   $217.82   $217.80   $217.80  
  Purchase #6 $249.69   4.499%   $260.9236   $260.92   $260.90   $260.90  
  Purchase #7 $63.40   7.712%   $68.2894   $68.29   $68.30   $68.30  
  7 purchase totals = $983.57       $1,064.6488   $1,064.63   $1,064.60   $1,064.50