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 $224.65   13.314%   $254.5599   $254.56   $254.55   $254.60  
  Purchase #2 $52.53   10.873%   $58.2416   $58.24   $58.25   $58.20  
  Purchase #3 $136.76   12.262%   $153.5295   $153.53   $153.55   $153.50  
  Purchase #4 $246.28   6.224%   $261.6085   $261.61   $261.60   $261.60  
  Purchase #5 $248.81   4.161%   $259.163   $259.16   $259.15   $259.20  
  Purchase #6 $76.66   13.204%   $86.7822   $86.78   $86.80   $86.80  
  Purchase #7 $95.96   4.303%   $100.0892   $100.09   $100.10   $100.10  
  7 purchase totals = $1,081.65       $1,173.9739   $1,173.97   $1,174.00   $1,174.00