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	$41.56	3.177%	$42.8804	$42.88	$42.90	$42.90
Purchase #2	$173.68	10.324%	$191.6107	$191.61	$191.60	$191.60
Purchase #3	$230.58	5.344%	$242.9022	$242.90	$242.90	$242.90
Purchase #4	$239.79	11.105%	$266.4187	$266.42	$266.40	$266.40
Purchase #5	$49.50	10.596%	$54.745	$54.75	$54.75	$54.70
Purchase #6	$29.25	6.388%	$31.1185	$31.12	$31.10	$31.10
Purchase #7	$184.87	3.338%	$191.041	$191.04	$191.05	$191.00
7 purchase totals =	$949.23		$1,020.7165	$1,020.72	$1,020.70	$1,020.60