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	$159.66	8.680%	$173.5185	$173.52	$173.50	$173.50
Purchase #2	$33.75	13.640%	$38.3535	$38.35	$38.35	$38.40
Purchase #3	$59.95	9.556%	$65.6788	$65.68	$65.70	$65.70
Purchase #4	$55.75	8.637%	$60.5651	$60.57	$60.55	$60.60
Purchase #5	$119.72	3.152%	$123.4936	$123.49	$123.50	$123.50
Purchase #6	$185.72	10.350%	$204.942	$204.94	$204.95	$204.90
Purchase #7	$172.62	6.168%	$183.2672	$183.27	$183.25	$183.30
7 purchase totals =	$787.17		$849.8187	$849.82	$849.80	$849.90