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 $67.53   13.669%   $76.7607   $76.76   $76.75   $76.80  
  Purchase #2 $47.28   7.745%   $50.9418   $50.94   $50.95   $50.90  
  Purchase #3 $88.96   12.242%   $99.8505   $99.85   $99.85   $99.90  
  Purchase #4 $101.57   12.661%   $114.4298   $114.43   $114.45   $114.40  
  Purchase #5 $233.90   6.710%   $249.5947   $249.59   $249.60   $249.60  
  Purchase #6 $199.53   3.543%   $206.5993   $206.60   $206.60   $206.60  
  Purchase #7 $194.71   7.852%   $209.9986   $210.00   $210.00   $210.00  
  7 purchase totals = $933.48       $1,008.1754   $1,008.17   $1,008.20   $1,008.20