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	$241.92	5.664%	$255.6223	$255.62	$255.60	$255.60
Purchase #2	$158.45	11.471%	$176.6258	$176.63	$176.65	$176.60
Purchase #3	$238.53	12.841%	$269.1596	$269.16	$269.15	$269.20
Purchase #4	$152.79	13.774%	$173.8353	$173.84	$173.85	$173.80
Purchase #5	$92.29	13.602%	$104.8433	$104.84	$104.85	$104.80
Purchase #6	$12.56	4.851%	$13.1693	$13.17	$13.15	$13.20
Purchase #7	$29.68	11.634%	$33.133	$33.13	$33.15	$33.10
7 purchase totals =	$926.22		$1,026.3886	$1,026.39	$1,026.40	$1,026.30