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	$20.45	5.618%	$21.5989	$21.60	$21.60	$21.60
Purchase #2	$15.71	9.666%	$17.2285	$17.23	$17.25	$17.20
Purchase #3	$233.32	13.292%	$264.3329	$264.33	$264.35	$264.30
Purchase #4	$144.61	10.248%	$159.4296	$159.43	$159.45	$159.40
Purchase #5	$189.38	13.446%	$214.844	$214.84	$214.85	$214.80
Purchase #6	$48.30	10.635%	$53.4367	$53.44	$53.45	$53.40
Purchase #7	$223.83	4.288%	$233.4278	$233.43	$233.45	$233.40
7 purchase totals =	$875.60		$964.2984	$964.30	$964.40	$964.10