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	$82.38	13.176%	$93.2344	$93.23	$93.25	$93.20
Purchase #2	$86.47	3.619%	$89.5993	$89.60	$89.60	$89.60
Purchase #3	$19.32	6.406%	$20.5576	$20.56	$20.55	$20.60
Purchase #4	$126.78	9.634%	$138.994	$138.99	$139.00	$139.00
Purchase #5	$77.88	11.613%	$86.9242	$86.92	$86.90	$86.90
Purchase #6	$42.65	13.807%	$48.5387	$48.54	$48.55	$48.50
Purchase #7	$160.31	8.350%	$173.6959	$173.70	$173.70	$173.70
7 purchase totals =	$595.79		$651.5441	$651.54	$651.55	$651.50