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	$96.73	4.209%	$100.8014	$100.80	$100.80	$100.80
Purchase #2	$50.95	13.677%	$57.9184	$57.92	$57.90	$57.90
Purchase #3	$247.37	6.647%	$263.8127	$263.81	$263.80	$263.80
Purchase #4	$157.52	9.286%	$172.1473	$172.15	$172.15	$172.10
Purchase #5	$58.62	12.587%	$65.9985	$66.00	$66.00	$66.00
Purchase #6	$139.40	13.810%	$158.6511	$158.65	$158.65	$158.70
Purchase #7	$38.28	12.137%	$42.926	$42.93	$42.95	$42.90
7 purchase totals =	$788.87		$862.2554	$862.26	$862.25	$862.20