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 $240.81   3.475%   $249.1781   $249.18   $249.20   $249.20  
  Purchase #2 $44.62   10.673%   $49.3823   $49.38   $49.40   $49.40  
  Purchase #3 $52.92   3.783%   $54.922   $54.92   $54.90   $54.90  
  Purchase #4 $229.51   6.547%   $244.536   $244.54   $244.55   $244.50  
  Purchase #5 $160.63   4.772%   $168.2953   $168.30   $168.30   $168.30  
  Purchase #6 $72.97   5.194%   $76.7601   $76.76   $76.75   $76.80  
  Purchase #7 $158.79   7.748%   $171.093   $171.09   $171.10   $171.10  
  7 purchase totals = $960.25       $1,014.1668   $1,014.17   $1,014.20   $1,014.20