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 $196.48   11.851%   $219.7648   $219.76   $219.75   $219.80  
  Purchase #2 $119.62   4.157%   $124.5926   $124.59   $124.60   $124.60  
  Purchase #3 $248.29   9.811%   $272.6497   $272.65   $272.65   $272.60  
  Purchase #4 $132.69   6.185%   $140.8969   $140.90   $140.90   $140.90  
  Purchase #5 $183.81   3.492%   $190.2286   $190.23   $190.25   $190.20  
  Purchase #6 $64.40   5.414%   $67.8866   $67.89   $67.90   $67.90  
  Purchase #7 $226.25   3.229%   $233.5556   $233.56   $233.55   $233.60  
  7 purchase totals = $1,171.54       $1,249.5748   $1,249.58   $1,249.60   $1,249.60