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	$66.47	4.507%	$69.4658	$69.47	$69.45	$69.50
Purchase #2	$237.59	11.145%	$264.0694	$264.07	$264.05	$264.10
Purchase #3	$48.52	13.195%	$54.9222	$54.92	$54.90	$54.90
Purchase #4	$34.39	13.489%	$39.0289	$39.03	$39.05	$39.00
Purchase #5	$196.46	9.470%	$215.0648	$215.06	$215.05	$215.10
Purchase #6	$70.76	13.750%	$80.4895	$80.49	$80.50	$80.50
Purchase #7	$46.69	10.335%	$51.5154	$51.52	$51.50	$51.50
7 purchase totals =	$700.88		$774.5560	$774.56	$774.50	$774.60