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 $60.99   4.853%   $63.9498   $63.95   $63.95   $63.90  
  Purchase #2 $127.61   13.258%   $144.5285   $144.53   $144.55   $144.50  
  Purchase #3 $134.71   10.388%   $148.7037   $148.70   $148.70   $148.70  
  Purchase #4 $201.45   9.409%   $220.4044   $220.40   $220.40   $220.40  
  Purchase #5 $83.31   10.805%   $92.3116   $92.31   $92.30   $92.30  
  Purchase #6 $9.48   5.661%   $10.0167   $10.02   $10.00   $10.00  
  Purchase #7 $131.41   8.801%   $142.9754   $142.98   $143.00   $143.00  
  7 purchase totals = $748.96       $822.8901   $822.89   $822.90   $822.80