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	$190.86	11.818%	$213.4158	$213.42	$213.40	$213.40
Purchase #2	$151.85	4.149%	$158.1503	$158.15	$158.15	$158.20
Purchase #3	$154.44	3.439%	$159.7512	$159.75	$159.75	$159.80
Purchase #4	$25.98	5.242%	$27.3419	$27.34	$27.35	$27.30
Purchase #5	$247.74	7.393%	$266.0554	$266.06	$266.05	$266.10
Purchase #6	$173.83	13.240%	$196.8451	$196.85	$196.85	$196.80
Purchase #7	$139.51	3.395%	$144.2464	$144.25	$144.25	$144.20
7 purchase totals =	$1,084.21		$1,165.8061	$1,165.82	$1,165.80	$1,165.80