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 $60.64   4.213%   $63.1948   $63.19   $63.20   $63.20  
  Purchase #2 $170.76   9.453%   $186.9019   $186.90   $186.90   $186.90  
  Purchase #3 $168.63   5.489%   $177.8861   $177.89   $177.90   $177.90  
  Purchase #4 $244.28   4.826%   $256.069   $256.07   $256.05   $256.10  
  Purchase #5 $32.46   13.383%   $36.8041   $36.80   $36.80   $36.80  
  Purchase #6 $32.48   7.742%   $34.9946   $34.99   $35.00   $35.00  
  Purchase #7 $134.38   4.802%   $140.8329   $140.83   $140.85   $140.80  
  7 purchase totals = $843.63       $896.6834   $896.67   $896.70   $896.70