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 $93.81   5.172%   $98.6619   $98.66   $98.65   $98.70  
  Purchase #2 $50.91   9.228%   $55.608   $55.61   $55.60   $55.60  
  Purchase #3 $182.80   7.358%   $196.2504   $196.25   $196.25   $196.30  
  Purchase #4 $189.82   6.657%   $202.4563   $202.46   $202.45   $202.50  
  Purchase #5 $135.42   11.859%   $151.4795   $151.48   $151.50   $151.50  
  Purchase #6 $51.66   7.537%   $55.5536   $55.55   $55.55   $55.60  
  Purchase #7 $117.36   8.193%   $126.9753   $126.98   $127.00   $127.00  
  7 purchase totals = $821.78       $886.9850   $886.99   $887.00   $887.20