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 $244.84   6.704%   $261.2541   $261.25   $261.25   $261.30  
  Purchase #2 $38.62   5.102%   $40.5904   $40.59   $40.60   $40.60  
  Purchase #3 $178.76   3.186%   $184.4553   $184.46   $184.45   $184.50  
  Purchase #4 $69.80   13.175%   $78.9962   $79.00   $79.00   $79.00  
  Purchase #5 $60.33   5.579%   $63.6958   $63.70   $63.70   $63.70  
  Purchase #6 $17.58   9.558%   $19.2603   $19.26   $19.25   $19.30  
  Purchase #7 $70.36   7.187%   $75.4168   $75.42   $75.40   $75.40  
  7 purchase totals = $680.29       $723.6689   $723.68   $723.65   $723.80