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	$45.99	11.246%	$51.162	$51.16	$51.15	$51.20
Purchase #2	$38.82	12.198%	$43.5553	$43.56	$43.55	$43.60
Purchase #3	$9.99	6.338%	$10.6232	$10.62	$10.60	$10.60
Purchase #4	$84.39	9.206%	$92.1589	$92.16	$92.15	$92.20
Purchase #5	$87.92	12.727%	$99.1096	$99.11	$99.10	$99.10
Purchase #6	$158.96	13.500%	$180.4196	$180.42	$180.40	$180.40
Purchase #7	$95.71	4.418%	$99.9385	$99.94	$99.95	$99.90
7 purchase totals =	$521.78		$576.9671	$576.97	$576.90	$577.00