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	$137.83	12.567%	$155.1511	$155.15	$155.15	$155.20
Purchase #2	$8.96	8.194%	$9.6942	$9.69	$9.70	$9.70
Purchase #3	$94.45	9.128%	$103.0714	$103.07	$103.05	$103.10
Purchase #4	$46.74	8.825%	$50.8648	$50.86	$50.85	$50.90
Purchase #5	$51.27	4.195%	$53.4208	$53.42	$53.40	$53.40
Purchase #6	$98.49	13.196%	$111.4867	$111.49	$111.50	$111.50
Purchase #7	$140.74	4.516%	$147.0958	$147.10	$147.10	$147.10
7 purchase totals =	$578.48		$630.7848	$630.78	$630.75	$630.90