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 $57.82   12.815%   $65.2296   $65.23   $65.25   $65.20  
  Purchase #2 $192.66   8.360%   $208.7664   $208.77   $208.75   $208.80  
  Purchase #3 $239.26   7.367%   $256.8863   $256.89   $256.90   $256.90  
  Purchase #4 $240.54   7.600%   $258.821   $258.82   $258.80   $258.80  
  Purchase #5 $35.66   10.421%   $39.3761   $39.38   $39.40   $39.40  
  Purchase #6 $98.37   6.215%   $104.4837   $104.48   $104.50   $104.50  
  Purchase #7 $92.40   3.859%   $95.9657   $95.97   $95.95   $96.00  
  7 purchase totals = $956.71       $1,029.5288   $1,029.54   $1,029.55   $1,029.60