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 $220.33   9.147%   $240.4836   $240.48   $240.50   $240.50  
  Purchase #2 $179.65   10.463%   $198.4468   $198.45   $198.45   $198.40  
  Purchase #3 $224.48   5.620%   $237.0958   $237.10   $237.10   $237.10  
  Purchase #4 $7.29   5.666%   $7.7031   $7.70   $7.70   $7.70  
  Purchase #5 $38.26   6.236%   $40.6459   $40.65   $40.65   $40.60  
  Purchase #6 $26.82   13.575%   $30.4608   $30.46   $30.45   $30.50  
  Purchase #7 $71.71   4.157%   $74.691   $74.69   $74.70   $74.70  
  7 purchase totals = $768.54       $829.5270   $829.53   $829.55   $829.50