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	$111.70	6.337%	$118.7784	$118.78	$118.80	$118.80
Purchase #2	$34.84	10.559%	$38.5188	$38.52	$38.50	$38.50
Purchase #3	$137.58	13.195%	$155.7337	$155.73	$155.75	$155.70
Purchase #4	$33.65	10.413%	$37.154	$37.15	$37.15	$37.20
Purchase #5	$29.46	9.174%	$32.1627	$32.16	$32.15	$32.20
Purchase #6	$80.39	7.626%	$86.5205	$86.52	$86.50	$86.50
Purchase #7	$153.41	3.649%	$159.0079	$159.01	$159.00	$159.00
7 purchase totals =	$581.03		$627.8760	$627.87	$627.85	$627.90