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 $23.53   11.357%   $26.2023   $26.20   $26.20   $26.20  
  Purchase #2 $36.48   13.791%   $41.511   $41.51   $41.50   $41.50  
  Purchase #3 $60.36   10.161%   $66.4932   $66.49   $66.50   $66.50  
  Purchase #4 $54.30   4.771%   $56.8907   $56.89   $56.90   $56.90  
  Purchase #5 $51.86   11.382%   $57.7627   $57.76   $57.75   $57.80  
  Purchase #6 $242.61   11.491%   $270.4883   $270.49   $270.50   $270.50  
  Purchase #7 $29.70   13.598%   $33.7386   $33.74   $33.75   $33.70  
  7 purchase totals = $498.84       $553.0868   $553.08   $553.10   $553.10