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	$15.52	3.842%	$16.1163	$16.12	$16.10	$16.10
Purchase #2	$105.86	5.556%	$111.7416	$111.74	$111.75	$111.70
Purchase #3	$132.52	10.857%	$146.9077	$146.91	$146.90	$146.90
Purchase #4	$230.31	12.108%	$258.1959	$258.20	$258.20	$258.20
Purchase #5	$81.26	9.613%	$89.0715	$89.07	$89.05	$89.10
Purchase #6	$135.72	4.222%	$141.4501	$141.45	$141.45	$141.50
Purchase #7	$46.95	11.534%	$52.3652	$52.37	$52.35	$52.40
7 purchase totals =	$748.14		$815.8483	$815.86	$815.80	$815.90