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 $24.78   4.644%   $25.9308   $25.93   $25.95   $25.90  
  Purchase #2 $248.39   8.674%   $269.9353   $269.94   $269.95   $269.90  
  Purchase #3 $86.67   12.849%   $97.8062   $97.81   $97.80   $97.80  
  Purchase #4 $87.78   12.856%   $99.065   $99.07   $99.05   $99.10  
  Purchase #5 $109.44   4.518%   $114.3845   $114.38   $114.40   $114.40  
  Purchase #6 $137.48   6.770%   $146.7874   $146.79   $146.80   $146.80  
  Purchase #7 $187.38   7.211%   $200.892   $200.89   $200.90   $200.90  
  7 purchase totals = $881.92       $954.8012   $954.81   $954.85   $954.80