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	$120.89	10.287%	$133.326	$133.33	$133.35	$133.30
Purchase #2	$111.57	10.242%	$122.997	$123.00	$123.00	$123.00
Purchase #3	$242.64	8.168%	$262.4588	$262.46	$262.45	$262.50
Purchase #4	$41.85	11.146%	$46.5146	$46.51	$46.50	$46.50
Purchase #5	$60.96	8.160%	$65.9343	$65.93	$65.95	$65.90
Purchase #6	$37.62	12.780%	$42.4278	$42.43	$42.45	$42.40
Purchase #7	$10.70	3.368%	$11.0604	$11.06	$11.05	$11.10
7 purchase totals =	$626.23		$684.7189	$684.72	$684.75	$684.70