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 $244.77   6.826%   $261.478   $261.48   $261.50   $261.50  
  Purchase #2 $14.33   12.769%   $16.1598   $16.16   $16.15   $16.20  
  Purchase #3 $250.41   13.649%   $284.5885   $284.59   $284.60   $284.60  
  Purchase #4 $248.81   13.561%   $282.5511   $282.55   $282.55   $282.60  
  Purchase #5 $118.71   9.551%   $130.048   $130.05   $130.05   $130.00  
  Purchase #6 $63.34   11.299%   $70.4968   $70.50   $70.50   $70.50  
  Purchase #7 $105.74   9.536%   $115.8234   $115.82   $115.80   $115.80  
  7 purchase totals = $1,046.11       $1,161.1456   $1,161.15   $1,161.15   $1,161.20