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	$97.51	9.613%	$106.8836	$106.88	$106.90	$106.90
Purchase #2	$57.72	7.470%	$62.0317	$62.03	$62.05	$62.00
Purchase #3	$122.40	4.135%	$127.4612	$127.46	$127.45	$127.50
Purchase #4	$166.60	10.329%	$183.8081	$183.81	$183.80	$183.80
Purchase #5	$10.91	4.729%	$11.4259	$11.43	$11.45	$11.40
Purchase #6	$132.50	10.809%	$146.8219	$146.82	$146.80	$146.80
Purchase #7	$64.88	13.731%	$73.7887	$73.79	$73.80	$73.80
7 purchase totals =	$652.52		$712.2211	$712.22	$712.25	$712.20