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 $52.53   11.655%   $58.6524   $58.65   $58.65   $58.70  
  Purchase #2 $195.38   11.102%   $217.0711   $217.07   $217.05   $217.10  
  Purchase #3 $185.51   9.157%   $202.4972   $202.50   $202.50   $202.50  
  Purchase #4 $102.48   11.246%   $114.0049   $114.00   $114.00   $114.00  
  Purchase #5 $21.86   8.605%   $23.7411   $23.74   $23.75   $23.70  
  Purchase #6 $87.78   11.124%   $97.5446   $97.54   $97.55   $97.50  
  Purchase #7 $227.49   13.665%   $258.5765   $258.58   $258.60   $258.60  
  7 purchase totals = $873.03       $972.0878   $972.08   $972.10   $972.10