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	$48.90	12.102%	$54.8179	$54.82	$54.80	$54.80
Purchase #2	$99.49	11.750%	$111.1801	$111.18	$111.20	$111.20
Purchase #3	$105.29	12.451%	$118.3997	$118.40	$118.40	$118.40
Purchase #4	$175.61	8.244%	$190.0873	$190.09	$190.10	$190.10
Purchase #5	$206.89	7.628%	$222.6716	$222.67	$222.65	$222.70
Purchase #6	$41.99	11.707%	$46.9058	$46.91	$46.90	$46.90
Purchase #7	$15.81	11.671%	$17.6552	$17.66	$17.65	$17.70
7 purchase totals =	$693.98		$761.7176	$761.73	$761.70	$761.80