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 $187.36   9.217%   $204.629   $204.63   $204.65   $204.60  
  Purchase #2 $239.32   9.382%   $261.773   $261.77   $261.75   $261.80  
  Purchase #3 $74.35   3.149%   $76.6913   $76.69   $76.70   $76.70  
  Purchase #4 $65.69   10.839%   $72.8101   $72.81   $72.80   $72.80  
  Purchase #5 $118.82   12.723%   $133.9375   $133.94   $133.95   $133.90  
  Purchase #6 $214.33   6.786%   $228.8744   $228.87   $228.85   $228.90  
  Purchase #7 $56.54   7.664%   $60.8732   $60.87   $60.85   $60.90  
  7 purchase totals = $956.41       $1,039.5885   $1,039.58   $1,039.55   $1,039.60