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	$82.73	9.122%	$90.2766	$90.28	$90.30	$90.30
Purchase #2	$48.68	11.434%	$54.2461	$54.25	$54.25	$54.20
Purchase #3	$26.27	12.104%	$29.4497	$29.45	$29.45	$29.40
Purchase #4	$226.50	9.224%	$247.3924	$247.39	$247.40	$247.40
Purchase #5	$107.62	3.617%	$111.5126	$111.51	$111.50	$111.50
Purchase #6	$105.85	4.413%	$110.5212	$110.52	$110.50	$110.50
Purchase #7	$21.88	8.553%	$23.7514	$23.75	$23.75	$23.80
7 purchase totals =	$619.53		$667.1500	$667.15	$667.15	$667.10