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 $95.86   13.453%   $108.756   $108.76   $108.75   $108.80  
  Purchase #2 $68.81   6.853%   $73.5255   $73.53   $73.55   $73.50  
  Purchase #3 $230.38   9.129%   $251.4114   $251.41   $251.40   $251.40  
  Purchase #4 $186.99   11.128%   $207.7982   $207.80   $207.80   $207.80  
  Purchase #5 $228.89   11.627%   $255.503   $255.50   $255.50   $255.50  
  Purchase #6 $160.59   5.385%   $169.2378   $169.24   $169.25   $169.20  
  Purchase #7 $124.76   12.528%   $140.3899   $140.39   $140.40   $140.40  
  7 purchase totals = $1,096.28       $1,206.6218   $1,206.63   $1,206.65   $1,206.60