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	$111.43	6.631%	$118.8189	$118.82	$118.80	$118.80
Purchase #2	$56.88	3.721%	$58.9965	$59.00	$59.00	$59.00
Purchase #3	$117.72	8.428%	$127.6414	$127.64	$127.65	$127.60
Purchase #4	$45.86	6.169%	$48.6891	$48.69	$48.70	$48.70
Purchase #5	$123.46	11.848%	$138.0875	$138.09	$138.10	$138.10
Purchase #6	$22.91	9.593%	$25.1078	$25.11	$25.10	$25.10
Purchase #7	$241.58	5.843%	$255.6955	$255.70	$255.70	$255.70
7 purchase totals =	$719.84		$773.0367	$773.05	$773.05	$773.00