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	$69.95	10.620%	$77.3787	$77.38	$77.40	$77.40
Purchase #2	$159.92	8.765%	$173.937	$173.94	$173.95	$173.90
Purchase #3	$176.52	11.118%	$196.1455	$196.15	$196.15	$196.10
Purchase #4	$93.91	7.852%	$101.2838	$101.28	$101.30	$101.30
Purchase #5	$117.45	13.125%	$132.8653	$132.87	$132.85	$132.90
Purchase #6	$110.38	11.710%	$123.3055	$123.31	$123.30	$123.30
Purchase #7	$52.83	3.466%	$54.6611	$54.66	$54.65	$54.70
7 purchase totals =	$780.96		$859.5769	$859.59	$859.60	$859.60