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 $236.42   7.862%   $255.0073   $255.01   $255.00   $255.00  
  Purchase #2 $6.98   8.388%   $7.5655   $7.57   $7.55   $7.60  
  Purchase #3 $235.94   8.617%   $256.2709   $256.27   $256.25   $256.30  
  Purchase #4 $32.67   4.710%   $34.2088   $34.21   $34.20   $34.20  
  Purchase #5 $162.75   5.127%   $171.0942   $171.09   $171.10   $171.10  
  Purchase #6 $172.35   8.128%   $186.3586   $186.36   $186.35   $186.40  
  Purchase #7 $46.75   12.302%   $52.5012   $52.50   $52.50   $52.50  
  7 purchase totals = $893.86       $963.0065   $963.01   $962.95   $963.10