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	$168.94	11.384%	$188.1721	$188.17	$188.15	$188.20
Purchase #2	$101.99	10.456%	$112.6541	$112.65	$112.65	$112.70
Purchase #3	$100.68	7.325%	$108.0548	$108.05	$108.05	$108.10
Purchase #4	$92.45	8.206%	$100.0364	$100.04	$100.05	$100.00
Purchase #5	$49.80	9.250%	$54.4065	$54.41	$54.40	$54.40
Purchase #6	$51.41	6.801%	$54.9064	$54.91	$54.90	$54.90
Purchase #7	$66.52	7.724%	$71.658	$71.66	$71.65	$71.70
7 purchase totals =	$631.79		$689.8883	$689.89	$689.85	$690.00