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 $181.49   11.457%   $202.2833   $202.28   $202.30   $202.30  
  Purchase #2 $221.65   8.363%   $240.1866   $240.19   $240.20   $240.20  
  Purchase #3 $41.53   11.423%   $46.274   $46.27   $46.25   $46.30  
  Purchase #4 $75.63   10.648%   $83.6831   $83.68   $83.70   $83.70  
  Purchase #5 $114.75   6.792%   $122.5438   $122.54   $122.55   $122.50  
  Purchase #6 $77.33   6.386%   $82.2683   $82.27   $82.25   $82.30  
  Purchase #7 $199.91   11.117%   $222.134   $222.13   $222.15   $222.10  
  7 purchase totals = $912.29       $999.3731   $999.36   $999.40   $999.40