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	$89.61	11.692%	$100.0872	$100.09	$100.10	$100.10
Purchase #2	$124.44	13.549%	$141.3004	$141.30	$141.30	$141.30
Purchase #3	$55.41	13.303%	$62.7812	$62.78	$62.80	$62.80
Purchase #4	$161.43	6.628%	$172.1296	$172.13	$172.15	$172.10
Purchase #5	$161.93	13.410%	$183.6448	$183.64	$183.65	$183.60
Purchase #6	$18.79	3.422%	$19.433	$19.43	$19.45	$19.40
Purchase #7	$92.62	4.199%	$96.5091	$96.51	$96.50	$96.50
7 purchase totals =	$704.23		$775.8853	$775.88	$775.95	$775.80