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	$122.60	4.215%	$127.7676	$127.77	$127.75	$127.80
Purchase #2	$6.55	10.271%	$7.2228	$7.22	$7.20	$7.20
Purchase #3	$106.68	4.856%	$111.8604	$111.86	$111.85	$111.90
Purchase #4	$50.92	13.546%	$57.8176	$57.82	$57.80	$57.80
Purchase #5	$100.66	6.619%	$107.3227	$107.32	$107.30	$107.30
Purchase #6	$54.94	12.201%	$61.6432	$61.64	$61.65	$61.60
Purchase #7	$223.97	5.407%	$236.0801	$236.08	$236.10	$236.10
7 purchase totals =	$666.32		$709.7144	$709.71	$709.65	$709.70