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	$47.62	6.352%	$50.6448	$50.64	$50.65	$50.60
Purchase #2	$42.82	10.154%	$47.1679	$47.17	$47.15	$47.20
Purchase #3	$99.49	11.593%	$111.0239	$111.02	$111.00	$111.00
Purchase #4	$198.64	12.563%	$223.5951	$223.60	$223.60	$223.60
Purchase #5	$145.26	9.269%	$158.7241	$158.72	$158.70	$158.70
Purchase #6	$213.26	4.867%	$223.6394	$223.64	$223.65	$223.60
Purchase #7	$223.31	12.522%	$251.2729	$251.27	$251.25	$251.30
7 purchase totals =	$970.40		$1,066.0681	$1,066.06	$1,066.00	$1,066.00