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	$15.25	9.418%	$16.6862	$16.69	$16.70	$16.70
Purchase #2	$91.67	9.364%	$100.254	$100.25	$100.25	$100.30
Purchase #3	$118.37	9.108%	$129.1511	$129.15	$129.15	$129.20
Purchase #4	$183.40	13.526%	$208.2067	$208.21	$208.20	$208.20
Purchase #5	$228.28	11.130%	$253.6876	$253.69	$253.70	$253.70
Purchase #6	$111.79	13.709%	$127.1153	$127.12	$127.10	$127.10
Purchase #7	$111.46	10.870%	$123.5757	$123.58	$123.60	$123.60
7 purchase totals =	$860.22		$958.6766	$958.69	$958.70	$958.80