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	$44.71	13.446%	$50.7217	$50.72	$50.70	$50.70
Purchase #2	$219.89	13.117%	$248.733	$248.73	$248.75	$248.70
Purchase #3	$52.42	3.185%	$54.0896	$54.09	$54.10	$54.10
Purchase #4	$107.89	9.642%	$118.2928	$118.29	$118.30	$118.30
Purchase #5	$80.71	11.285%	$89.8181	$89.82	$89.80	$89.80
Purchase #6	$31.71	8.195%	$34.3086	$34.31	$34.30	$34.30
Purchase #7	$25.57	11.695%	$28.5604	$28.56	$28.55	$28.60
7 purchase totals =	$562.90		$624.5242	$624.52	$624.50	$624.50