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 $48.58   13.286%   $55.0343   $55.03   $55.05   $55.00  
  Purchase #2 $82.42   6.129%   $87.4715   $87.47   $87.45   $87.50  
  Purchase #3 $190.75   5.177%   $200.6251   $200.63   $200.65   $200.60  
  Purchase #4 $246.35   6.333%   $261.9513   $261.95   $261.95   $262.00  
  Purchase #5 $115.57   5.716%   $122.176   $122.18   $122.20   $122.20  
  Purchase #6 $51.29   4.418%   $53.556   $53.56   $53.55   $53.60  
  Purchase #7 $173.70   13.142%   $196.5277   $196.53   $196.55   $196.50  
  7 purchase totals = $908.66       $977.3419   $977.35   $977.40   $977.40