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 $153.69   9.496%   $168.2844   $168.28   $168.30   $168.30  
  Purchase #2 $236.91   10.212%   $261.1032   $261.10   $261.10   $261.10  
  Purchase #3 $213.78   6.116%   $226.8548   $226.85   $226.85   $226.90  
  Purchase #4 $196.99   3.675%   $204.2294   $204.23   $204.25   $204.20  
  Purchase #5 $73.69   13.533%   $83.6625   $83.66   $83.65   $83.70  
  Purchase #6 $216.33   4.468%   $225.9956   $226.00   $226.00   $226.00  
  Purchase #7 $176.64   7.590%   $190.047   $190.05   $190.05   $190.00  
  7 purchase totals = $1,268.03       $1,360.1769   $1,360.17   $1,360.20   $1,360.20