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 $26.98   9.725%   $29.6038   $29.60   $29.60   $29.60  
  Purchase #2 $230.98   4.581%   $241.5612   $241.56   $241.55   $241.60  
  Purchase #3 $62.38   4.817%   $65.3848   $65.38   $65.40   $65.40  
  Purchase #4 $187.26   5.467%   $197.4975   $197.50   $197.50   $197.50  
  Purchase #5 $248.44   5.260%   $261.5079   $261.51   $261.50   $261.50  
  Purchase #6 $51.55   7.230%   $55.2771   $55.28   $55.30   $55.30  
  Purchase #7 $41.59   4.362%   $43.4042   $43.40   $43.40   $43.40  
  7 purchase totals = $849.18       $894.2365   $894.23   $894.25   $894.30