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	$10.43	11.694%	$11.6497	$11.65	$11.65	$11.60
Purchase #2	$155.82	11.108%	$173.1285	$173.13	$173.15	$173.10
Purchase #3	$130.38	5.123%	$137.0594	$137.06	$137.05	$137.10
Purchase #4	$226.33	3.787%	$234.9011	$234.90	$234.90	$234.90
Purchase #5	$128.95	8.232%	$139.5652	$139.57	$139.55	$139.60
Purchase #6	$114.99	7.478%	$123.589	$123.59	$123.60	$123.60
Purchase #7	$40.95	11.619%	$45.708	$45.71	$45.70	$45.70
7 purchase totals =	$807.85		$865.6009	$865.61	$865.60	$865.60