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 $192.39   5.669%   $203.2966   $203.30   $203.30   $203.30  
  Purchase #2 $175.93   12.719%   $198.3065   $198.31   $198.30   $198.30  
  Purchase #3 $38.35   6.538%   $40.8573   $40.86   $40.85   $40.90  
  Purchase #4 $91.30   6.866%   $97.5687   $97.57   $97.55   $97.60  
  Purchase #5 $150.31   12.260%   $168.738   $168.74   $168.75   $168.70  
  Purchase #6 $210.61   7.432%   $226.2625   $226.26   $226.25   $226.30  
  Purchase #7 $208.64   4.726%   $218.5003   $218.50   $218.50   $218.50  
  7 purchase totals = $1,067.53       $1,153.5299   $1,153.54   $1,153.50   $1,153.60