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	$38.59	8.111%	$41.72	$41.72	$41.70	$41.70
Purchase #2	$117.77	12.307%	$132.264	$132.26	$132.25	$132.30
Purchase #3	$91.54	12.548%	$103.0264	$103.03	$103.05	$103.00
Purchase #4	$132.44	9.784%	$145.3979	$145.40	$145.40	$145.40
Purchase #5	$97.92	9.692%	$107.4104	$107.41	$107.40	$107.40
Purchase #6	$22.92	4.197%	$23.882	$23.88	$23.90	$23.90
Purchase #7	$99.60	11.611%	$111.1646	$111.16	$111.15	$111.20
7 purchase totals =	$600.78		$664.8653	$664.86	$664.85	$664.90