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	$48.92	12.376%	$54.9743	$54.97	$54.95	$55.00
Purchase #2	$10.68	9.814%	$11.7281	$11.73	$11.75	$11.70
Purchase #3	$103.92	9.196%	$113.4765	$113.48	$113.50	$113.50
Purchase #4	$237.73	7.328%	$255.1509	$255.15	$255.15	$255.20
Purchase #5	$55.60	10.438%	$61.4035	$61.40	$61.40	$61.40
Purchase #6	$99.67	11.808%	$111.439	$111.44	$111.45	$111.40
Purchase #7	$64.94	9.147%	$70.8801	$70.88	$70.90	$70.90
7 purchase totals =	$621.46		$679.0524	$679.05	$679.10	$679.10