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	$231.51	6.567%	$246.7133	$246.71	$246.70	$246.70
Purchase #2	$230.75	12.853%	$260.4083	$260.41	$260.40	$260.40
Purchase #3	$59.60	9.689%	$65.3746	$65.37	$65.35	$65.40
Purchase #4	$126.39	4.307%	$131.8336	$131.83	$131.85	$131.80
Purchase #5	$53.30	11.472%	$59.4146	$59.41	$59.40	$59.40
Purchase #6	$17.97	11.620%	$20.0581	$20.06	$20.05	$20.10
Purchase #7	$142.95	8.329%	$154.8563	$154.86	$154.85	$154.90
7 purchase totals =	$862.47		$938.6588	$938.65	$938.60	$938.70