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 $238.99   12.677%   $269.2868   $269.29   $269.30   $269.30  
  Purchase #2 $182.62   8.283%   $197.7464   $197.75   $197.75   $197.70  
  Purchase #3 $133.84   7.532%   $143.9208   $143.92   $143.90   $143.90  
  Purchase #4 $162.51   5.103%   $170.8029   $170.80   $170.80   $170.80  
  Purchase #5 $240.55   6.158%   $255.3631   $255.36   $255.35   $255.40  
  Purchase #6 $102.94   10.782%   $114.039   $114.04   $114.05   $114.00  
  Purchase #7 $242.80   4.389%   $253.4565   $253.46   $253.45   $253.50  
  7 purchase totals = $1,304.25       $1,404.6155   $1,404.62   $1,404.60   $1,404.60