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	$98.27	4.431%	$102.6243	$102.62	$102.60	$102.60
Purchase #2	$103.93	4.198%	$108.293	$108.29	$108.30	$108.30
Purchase #3	$247.77	4.634%	$259.2517	$259.25	$259.25	$259.30
Purchase #4	$205.38	9.678%	$225.2567	$225.26	$225.25	$225.30
Purchase #5	$9.92	9.210%	$10.8336	$10.83	$10.85	$10.80
Purchase #6	$111.39	11.152%	$123.8122	$123.81	$123.80	$123.80
Purchase #7	$233.76	8.639%	$253.9545	$253.95	$253.95	$254.00
7 purchase totals =	$1,010.42		$1,084.0260	$1,084.01	$1,084.00	$1,084.10