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	$239.60	5.280%	$252.2509	$252.25	$252.25	$252.30
Purchase #2	$161.54	7.341%	$173.3987	$173.40	$173.40	$173.40
Purchase #3	$195.30	13.531%	$221.726	$221.73	$221.75	$221.70
Purchase #4	$68.71	5.666%	$72.6031	$72.60	$72.60	$72.60
Purchase #5	$118.78	7.201%	$127.3333	$127.33	$127.35	$127.30
Purchase #6	$168.65	12.753%	$190.1579	$190.16	$190.15	$190.20
Purchase #7	$128.85	13.118%	$145.7525	$145.75	$145.75	$145.80
7 purchase totals =	$1,081.43		$1,183.2224	$1,183.22	$1,183.25	$1,183.30