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 $233.29   12.477%   $262.3976   $262.40   $262.40   $262.40  
  Purchase #2 $229.55   8.725%   $249.5782   $249.58   $249.60   $249.60  
  Purchase #3 $91.37   7.512%   $98.2337   $98.23   $98.25   $98.20  
  Purchase #4 $151.82   11.271%   $168.9316   $168.93   $168.95   $168.90  
  Purchase #5 $46.99   6.151%   $49.8804   $49.88   $49.90   $49.90  
  Purchase #6 $202.80   10.232%   $223.5505   $223.55   $223.55   $223.60  
  Purchase #7 $196.84   5.683%   $208.0264   $208.03   $208.05   $208.00  
  7 purchase totals = $1,152.66       $1,260.5984   $1,260.60   $1,260.70   $1,260.60