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 $168.87   6.116%   $179.1981   $179.20   $179.20   $179.20  
  Purchase #2 $150.83   3.708%   $156.4228   $156.42   $156.40   $156.40  
  Purchase #3 $65.99   11.840%   $73.8032   $73.80   $73.80   $73.80  
  Purchase #4 $231.28   6.142%   $245.4852   $245.49   $245.50   $245.50  
  Purchase #5 $28.81   5.435%   $30.3758   $30.38   $30.40   $30.40  
  Purchase #6 $161.25   8.268%   $174.5822   $174.58   $174.60   $174.60  
  Purchase #7 $55.77   7.873%   $60.1608   $60.16   $60.15   $60.20  
  7 purchase totals = $862.80       $920.0281   $920.03   $920.05   $920.10