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	$100.52	10.849%	$111.4254	$111.43	$111.45	$111.40
Purchase #2	$214.29	11.252%	$238.4019	$238.40	$238.40	$238.40
Purchase #3	$19.45	4.641%	$20.3527	$20.35	$20.35	$20.40
Purchase #4	$130.92	5.729%	$138.4204	$138.42	$138.40	$138.40
Purchase #5	$39.44	5.415%	$41.5757	$41.58	$41.60	$41.60
Purchase #6	$13.42	12.602%	$15.1112	$15.11	$15.10	$15.10
Purchase #7	$243.52	6.194%	$258.6036	$258.60	$258.60	$258.60
7 purchase totals =	$761.56		$823.8909	$823.89	$823.90	$823.90