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	$38.41	10.148%	$42.3078	$42.31	$42.30	$42.30
Purchase #2	$89.66	7.313%	$96.2168	$96.22	$96.20	$96.20
Purchase #3	$35.85	7.189%	$38.4273	$38.43	$38.45	$38.40
Purchase #4	$193.31	13.332%	$219.0821	$219.08	$219.10	$219.10
Purchase #5	$210.83	9.429%	$230.7092	$230.71	$230.70	$230.70
Purchase #6	$48.36	13.168%	$54.728	$54.73	$54.75	$54.70
Purchase #7	$42.95	7.192%	$46.039	$46.04	$46.05	$46.00
7 purchase totals =	$659.37		$727.5102	$727.52	$727.55	$727.40