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	$12.77	7.451%	$13.7215	$13.72	$13.70	$13.70
Purchase #2	$100.38	3.664%	$104.0579	$104.06	$104.05	$104.10
Purchase #3	$102.91	8.361%	$111.5143	$111.51	$111.50	$111.50
Purchase #4	$68.79	12.259%	$77.223	$77.22	$77.20	$77.20
Purchase #5	$151.28	13.721%	$172.0371	$172.04	$172.05	$172.00
Purchase #6	$46.54	13.406%	$52.7792	$52.78	$52.80	$52.80
Purchase #7	$224.49	12.569%	$252.7061	$252.71	$252.70	$252.70
7 purchase totals =	$707.16		$784.0391	$784.04	$784.00	$784.00