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 $239.43   3.809%   $248.5499   $248.55   $248.55   $248.50  
  Purchase #2 $53.25   9.624%   $58.3748   $58.37   $58.35   $58.40  
  Purchase #3 $235.87   10.844%   $261.4477   $261.45   $261.45   $261.40  
  Purchase #4 $37.27   13.790%   $42.4095   $42.41   $42.40   $42.40  
  Purchase #5 $56.81   6.628%   $60.5754   $60.58   $60.60   $60.60  
  Purchase #6 $239.49   10.682%   $265.0723   $265.07   $265.05   $265.10  
  Purchase #7 $76.43   13.352%   $86.6349   $86.63   $86.65   $86.60  
  7 purchase totals = $938.55       $1,023.0645   $1,023.06   $1,023.05   $1,023.00