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 $63.78   4.270%   $66.5034   $66.50   $66.50   $66.50  
  Purchase #2 $85.57   8.340%   $92.7065   $92.71   $92.70   $92.70  
  Purchase #3 $91.93   5.752%   $97.2178   $97.22   $97.20   $97.20  
  Purchase #4 $146.56   6.295%   $155.786   $155.79   $155.80   $155.80  
  Purchase #5 $231.50   13.128%   $261.8913   $261.89   $261.90   $261.90  
  Purchase #6 $125.32   6.522%   $133.4934   $133.49   $133.50   $133.50  
  Purchase #7 $193.61   12.271%   $217.3679   $217.37   $217.35   $217.40  
  7 purchase totals = $938.27       $1,024.9663   $1,024.97   $1,024.95   $1,025.00