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 $236.97   10.548%   $261.9656   $261.97   $261.95   $262.00  
  Purchase #2 $153.44   7.204%   $164.4938   $164.49   $164.50   $164.50  
  Purchase #3 $35.35   3.420%   $36.559   $36.56   $36.55   $36.60  
  Purchase #4 $131.92   3.163%   $136.0926   $136.09   $136.10   $136.10  
  Purchase #5 $181.45   8.287%   $196.4868   $196.49   $196.50   $196.50  
  Purchase #6 $141.78   4.342%   $147.9361   $147.94   $147.95   $147.90  
  Purchase #7 $23.41   3.437%   $24.2146   $24.21   $24.20   $24.20  
  7 purchase totals = $904.32       $967.7485   $967.75   $967.75   $967.80