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	$49.90	9.590%	$54.6854	$54.69	$54.70	$54.70
Purchase #2	$243.60	4.839%	$255.3878	$255.39	$255.40	$255.40
Purchase #3	$107.79	3.513%	$111.5767	$111.58	$111.60	$111.60
Purchase #4	$215.83	5.146%	$226.9366	$226.94	$226.95	$226.90
Purchase #5	$25.36	8.856%	$27.6059	$27.61	$27.60	$27.60
Purchase #6	$115.99	12.449%	$130.4296	$130.43	$130.45	$130.40
Purchase #7	$214.52	12.371%	$241.0583	$241.06	$241.05	$241.10
7 purchase totals =	$972.99		$1,047.6803	$1,047.70	$1,047.75	$1,047.70