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	$165.34	4.509%	$172.7952	$172.80	$172.80	$172.80
Purchase #2	$116.89	3.862%	$121.4043	$121.40	$121.40	$121.40
Purchase #3	$77.90	8.201%	$84.2886	$84.29	$84.30	$84.30
Purchase #4	$248.87	12.288%	$279.4511	$279.45	$279.45	$279.50
Purchase #5	$244.43	12.801%	$275.7195	$275.72	$275.70	$275.70
Purchase #6	$166.47	13.459%	$188.8752	$188.88	$188.90	$188.90
Purchase #7	$94.72	9.684%	$103.8927	$103.89	$103.90	$103.90
7 purchase totals =	$1,114.62		$1,226.4266	$1,226.43	$1,226.45	$1,226.50