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	$38.88	11.813%	$43.4729	$43.47	$43.45	$43.50
Purchase #2	$123.35	9.186%	$134.6809	$134.68	$134.70	$134.70
Purchase #3	$117.39	7.468%	$126.1567	$126.16	$126.15	$126.20
Purchase #4	$155.54	11.488%	$173.4084	$173.41	$173.40	$173.40
Purchase #5	$117.89	13.247%	$133.5069	$133.51	$133.50	$133.50
Purchase #6	$14.88	3.690%	$15.4291	$15.43	$15.45	$15.40
Purchase #7	$80.65	12.599%	$90.8111	$90.81	$90.80	$90.80
7 purchase totals =	$648.58		$717.4660	$717.47	$717.45	$717.50