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 $57.66   12.751%   $65.0122   $65.01   $65.00   $65.00  
  Purchase #2 $242.49   8.299%   $262.6142   $262.61   $262.60   $262.60  
  Purchase #3 $79.69   8.541%   $86.4963   $86.50   $86.50   $86.50  
  Purchase #4 $159.39   7.637%   $171.5626   $171.56   $171.55   $171.60  
  Purchase #5 $87.70   5.796%   $92.7831   $92.78   $92.80   $92.80  
  Purchase #6 $133.68   10.726%   $148.0185   $148.02   $148.00   $148.00  
  Purchase #7 $164.92   4.664%   $172.6119   $172.61   $172.60   $172.60  
  7 purchase totals = $925.53       $999.0988   $999.09   $999.05   $999.10