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 $119.82   5.650%   $126.5898   $126.59   $126.60   $126.60  
  Purchase #2 $132.26   8.607%   $143.6436   $143.64   $143.65   $143.60  
  Purchase #3 $114.40   10.379%   $126.2736   $126.27   $126.25   $126.30  
  Purchase #4 $176.48   12.662%   $198.8259   $198.83   $198.85   $198.80  
  Purchase #5 $186.72   10.733%   $206.7607   $206.76   $206.75   $206.80  
  Purchase #6 $117.28   6.754%   $125.2011   $125.20   $125.20   $125.20  
  Purchase #7 $53.74   7.204%   $57.6114   $57.61   $57.60   $57.60  
  7 purchase totals = $900.70       $984.9061   $984.90   $984.90   $984.90