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 $248.64   5.142%   $261.4251   $261.43   $261.45   $261.40  
  Purchase #2 $250.49   9.667%   $274.7049   $274.70   $274.70   $274.70  
  Purchase #3 $184.34   8.595%   $200.184   $200.18   $200.20   $200.20  
  Purchase #4 $48.61   8.318%   $52.6534   $52.65   $52.65   $52.70  
  Purchase #5 $222.91   8.314%   $241.4427   $241.44   $241.45   $241.40  
  Purchase #6 $138.40   4.735%   $144.9532   $144.95   $144.95   $145.00  
  Purchase #7 $75.60   9.637%   $82.8856   $82.89   $82.90   $82.90  
  7 purchase totals = $1,168.99       $1,258.2489   $1,258.24   $1,258.30   $1,258.30