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 $114.96   4.102%   $119.6757   $119.68   $119.70   $119.70  
  Purchase #2 $168.72   8.291%   $182.7086   $182.71   $182.70   $182.70  
  Purchase #3 $187.59   6.406%   $199.607   $199.61   $199.60   $199.60  
  Purchase #4 $190.31   13.614%   $216.2188   $216.22   $216.20   $216.20  
  Purchase #5 $15.66   10.372%   $17.2843   $17.28   $17.30   $17.30  
  Purchase #6 $88.31   6.468%   $94.0219   $94.02   $94.00   $94.00  
  Purchase #7 $32.49   9.749%   $35.6575   $35.66   $35.65   $35.70  
  7 purchase totals = $798.04       $865.1738   $865.18   $865.15   $865.20