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 $54.75   13.606%   $62.1993   $62.20   $62.20   $62.20  
  Purchase #2 $208.67   5.699%   $220.5621   $220.56   $220.55   $220.60  
  Purchase #3 $29.38   4.289%   $30.6401   $30.64   $30.65   $30.60  
  Purchase #4 $65.87   9.149%   $71.8964   $71.90   $71.90   $71.90  
  Purchase #5 $165.33   5.486%   $174.4   $174.40   $174.40   $174.40  
  Purchase #6 $123.89   13.223%   $140.272   $140.27   $140.25   $140.30  
  Purchase #7 $198.86   3.872%   $206.5599   $206.56   $206.55   $206.60  
  7 purchase totals = $846.75       $906.5298   $906.53   $906.50   $906.60