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	$107.32	3.831%	$111.4314	$111.43	$111.45	$111.40
Purchase #2	$17.63	4.519%	$18.4267	$18.43	$18.45	$18.40
Purchase #3	$13.50	11.105%	$14.9992	$15.00	$15.00	$15.00
Purchase #4	$20.62	6.163%	$21.8908	$21.89	$21.90	$21.90
Purchase #5	$107.50	8.196%	$116.3107	$116.31	$116.30	$116.30
Purchase #6	$80.44	10.692%	$89.0406	$89.04	$89.05	$89.00
Purchase #7	$212.29	5.336%	$223.6178	$223.62	$223.60	$223.60
7 purchase totals =	$559.30		$595.7172	$595.72	$595.75	$595.60