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 $59.66   10.242%   $65.7704   $65.77   $65.75   $65.80  
  Purchase #2 $249.36   4.689%   $261.0525   $261.05   $261.05   $261.10  
  Purchase #3 $205.27   4.628%   $214.7699   $214.77   $214.75   $214.80  
  Purchase #4 $168.95   13.503%   $191.7633   $191.76   $191.75   $191.80  
  Purchase #5 $199.42   3.418%   $206.2362   $206.24   $206.25   $206.20  
  Purchase #6 $149.69   13.306%   $169.6078   $169.61   $169.60   $169.60  
  Purchase #7 $16.77   7.653%   $18.0534   $18.05   $18.05   $18.10  
  7 purchase totals = $1,049.12       $1,127.2535   $1,127.25   $1,127.20   $1,127.40