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	$81.80	11.365%	$91.0966	$91.10	$91.10	$91.10
Purchase #2	$61.41	9.555%	$67.2777	$67.28	$67.30	$67.30
Purchase #3	$10.37	3.111%	$10.6926	$10.69	$10.70	$10.70
Purchase #4	$14.95	3.226%	$15.4323	$15.43	$15.45	$15.40
Purchase #5	$176.47	13.423%	$200.1576	$200.16	$200.15	$200.20
Purchase #6	$102.58	5.113%	$107.8249	$107.82	$107.80	$107.80
Purchase #7	$158.69	4.361%	$165.6105	$165.61	$165.60	$165.60
7 purchase totals =	$606.27		$658.0922	$658.09	$658.10	$658.10