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 $96.63   13.433%   $109.6103   $109.61   $109.60   $109.60  
  Purchase #2 $60.46   6.177%   $64.1946   $64.19   $64.20   $64.20  
  Purchase #3 $186.32   3.463%   $192.7723   $192.77   $192.75   $192.80  
  Purchase #4 $30.99   13.411%   $35.1461   $35.15   $35.15   $35.10  
  Purchase #5 $104.97   3.767%   $108.9242   $108.92   $108.90   $108.90  
  Purchase #6 $103.26   13.773%   $117.482   $117.48   $117.50   $117.50  
  Purchase #7 $44.29   12.724%   $49.9255   $49.93   $49.95   $49.90  
  7 purchase totals = $626.92       $678.0550   $678.05   $678.05   $678.00