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	$11.90	3.411%	$12.3059	$12.31	$12.30	$12.30
Purchase #2	$183.83	8.105%	$198.7294	$198.73	$198.75	$198.70
Purchase #3	$93.50	13.793%	$106.3965	$106.40	$106.40	$106.40
Purchase #4	$47.36	6.103%	$50.2504	$50.25	$50.25	$50.30
Purchase #5	$180.76	5.189%	$190.1396	$190.14	$190.15	$190.10
Purchase #6	$19.43	11.687%	$21.7008	$21.70	$21.70	$21.70
Purchase #7	$115.98	9.784%	$127.3275	$127.33	$127.35	$127.30
7 purchase totals =	$652.76		$706.8501	$706.86	$706.90	$706.80