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 $61.99   6.582%   $66.0702   $66.07   $66.05   $66.10  
  Purchase #2 $41.95   4.548%   $43.8579   $43.86   $43.85   $43.90  
  Purchase #3 $176.85   6.692%   $188.6848   $188.68   $188.70   $188.70  
  Purchase #4 $65.82   5.660%   $69.5454   $69.55   $69.55   $69.50  
  Purchase #5 $156.43   3.481%   $161.8753   $161.88   $161.90   $161.90  
  Purchase #6 $140.51   11.786%   $157.0705   $157.07   $157.05   $157.10  
  Purchase #7 $179.41   3.201%   $185.1529   $185.15   $185.15   $185.20  
  7 purchase totals = $822.96       $872.2570   $872.26   $872.25   $872.40