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	$40.92	9.695%	$44.8872	$44.89	$44.90	$44.90
Purchase #2	$94.41	6.370%	$100.4239	$100.42	$100.40	$100.40
Purchase #3	$105.66	11.143%	$117.4337	$117.43	$117.45	$117.40
Purchase #4	$106.89	4.239%	$111.4211	$111.42	$111.40	$111.40
Purchase #5	$78.63	3.429%	$81.3262	$81.33	$81.35	$81.30
Purchase #6	$107.45	6.849%	$114.8093	$114.81	$114.80	$114.80
Purchase #7	$43.95	4.858%	$46.0851	$46.09	$46.10	$46.10
7 purchase totals =	$577.91		$616.3865	$616.39	$616.40	$616.30