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 $234.30   11.493%   $261.2281   $261.23   $261.25   $261.20  
  Purchase #2 $228.46   9.822%   $250.8993   $250.90   $250.90   $250.90  
  Purchase #3 $181.26   6.405%   $192.8697   $192.87   $192.85   $192.90  
  Purchase #4 $209.60   8.774%   $227.9903   $227.99   $228.00   $228.00  
  Purchase #5 $49.49   10.342%   $54.6083   $54.61   $54.60   $54.60  
  Purchase #6 $65.98   6.699%   $70.4   $70.40   $70.40   $70.40  
  Purchase #7 $196.66   4.102%   $204.727   $204.73   $204.75   $204.70  
  7 purchase totals = $1,165.75       $1,262.7227   $1,262.73   $1,262.75   $1,262.70