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 $185.95   5.208%   $195.6343   $195.63   $195.65   $195.60  
  Purchase #2 $137.80   3.179%   $142.1807   $142.18   $142.20   $142.20  
  Purchase #3 $145.69   8.814%   $158.5311   $158.53   $158.55   $158.50  
  Purchase #4 $54.36   10.161%   $59.8835   $59.88   $59.90   $59.90  
  Purchase #5 $30.60   12.255%   $34.35   $34.35   $34.35   $34.40  
  Purchase #6 $105.52   8.283%   $114.2602   $114.26   $114.25   $114.30  
  Purchase #7 $246.65   6.123%   $261.7524   $261.75   $261.75   $261.80  
  7 purchase totals = $906.57       $966.5922   $966.58   $966.65   $966.70