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	$7.33	4.836%	$7.6845	$7.68	$7.70	$7.70
Purchase #2	$230.78	12.156%	$258.8336	$258.83	$258.85	$258.80
Purchase #3	$93.92	11.528%	$104.7471	$104.75	$104.75	$104.70
Purchase #4	$98.27	13.491%	$111.5276	$111.53	$111.55	$111.50
Purchase #5	$247.45	12.500%	$278.3813	$278.38	$278.40	$278.40
Purchase #6	$31.39	12.139%	$35.2004	$35.20	$35.20	$35.20
Purchase #7	$85.37	6.451%	$90.8772	$90.88	$90.90	$90.90
7 purchase totals =	$794.51		$887.2517	$887.25	$887.35	$887.20