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 $65.46   6.493%   $69.7103   $69.71   $69.70   $69.70  
  Purchase #2 $112.95   4.696%   $118.2541   $118.25   $118.25   $118.30  
  Purchase #3 $15.74   12.536%   $17.7132   $17.71   $17.70   $17.70  
  Purchase #4 $99.83   8.186%   $108.0021   $108.00   $108.00   $108.00  
  Purchase #5 $23.62   13.223%   $26.7433   $26.74   $26.75   $26.70  
  Purchase #6 $126.47   3.255%   $130.5866   $130.59   $130.60   $130.60  
  Purchase #7 $241.81   4.214%   $251.9999   $252.00   $252.00   $252.00  
  7 purchase totals = $685.88       $723.0095   $723.00   $723.00   $723.00