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 $249.25   7.501%   $267.9462   $267.95   $267.95   $267.90  
  Purchase #2 $111.54   3.455%   $115.3937   $115.39   $115.40   $115.40  
  Purchase #3 $95.93   13.795%   $109.1635   $109.16   $109.15   $109.20  
  Purchase #4 $98.91   4.702%   $103.5607   $103.56   $103.55   $103.60  
  Purchase #5 $215.38   5.835%   $227.9474   $227.95   $227.95   $227.90  
  Purchase #6 $158.55   11.456%   $176.7135   $176.71   $176.70   $176.70  
  Purchase #7 $241.79   10.449%   $267.0546   $267.05   $267.05   $267.10  
  7 purchase totals = $1,171.35       $1,267.7796   $1,267.77   $1,267.75   $1,267.80