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 $44.27   11.440%   $49.3345   $49.33   $49.35   $49.30  
  Purchase #2 $101.51   12.359%   $114.0556   $114.06   $114.05   $114.10  
  Purchase #3 $165.42   3.493%   $171.1981   $171.20   $171.20   $171.20  
  Purchase #4 $243.33   13.374%   $275.873   $275.87   $275.85   $275.90  
  Purchase #5 $215.90   5.556%   $227.8954   $227.90   $227.90   $227.90  
  Purchase #6 $236.71   5.514%   $249.7622   $249.76   $249.75   $249.80  
  Purchase #7 $69.79   4.534%   $72.9543   $72.95   $72.95   $73.00  
  7 purchase totals = $1,076.93       $1,161.0731   $1,161.07   $1,161.05   $1,161.20