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 $216.48   9.312%   $236.6386   $236.64   $236.65   $236.60  
  Purchase #2 $119.40   11.792%   $133.4796   $133.48   $133.50   $133.50  
  Purchase #3 $60.76   13.383%   $68.8915   $68.89   $68.90   $68.90  
  Purchase #4 $95.47   7.457%   $102.5892   $102.59   $102.60   $102.60  
  Purchase #5 $242.82   5.289%   $255.6627   $255.66   $255.65   $255.70  
  Purchase #6 $91.73   6.531%   $97.7209   $97.72   $97.70   $97.70  
  Purchase #7 $56.98   12.786%   $64.2655   $64.27   $64.25   $64.30  
  7 purchase totals = $883.64       $959.2480   $959.25   $959.25   $959.30