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 $226.38   10.196%   $249.4617   $249.46   $249.45   $249.50  
  Purchase #2 $194.28   4.348%   $202.7273   $202.73   $202.75   $202.70  
  Purchase #3 $56.70   12.201%   $63.618   $63.62   $63.60   $63.60  
  Purchase #4 $91.42   7.853%   $98.5992   $98.60   $98.60   $98.60  
  Purchase #5 $151.83   3.486%   $157.1228   $157.12   $157.10   $157.10  
  Purchase #6 $59.68   3.334%   $61.6697   $61.67   $61.65   $61.70  
  Purchase #7 $14.48   4.225%   $15.0918   $15.09   $15.10   $15.10  
  7 purchase totals = $794.77       $848.2905   $848.29   $848.25   $848.30