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	$179.40	4.268%	$187.0568	$187.06	$187.05	$187.10
Purchase #2	$128.50	12.106%	$144.0562	$144.06	$144.05	$144.10
Purchase #3	$178.38	7.436%	$191.6443	$191.64	$191.65	$191.60
Purchase #4	$6.82	13.144%	$7.7164	$7.72	$7.70	$7.70
Purchase #5	$18.75	6.600%	$19.9875	$19.99	$20.00	$20.00
Purchase #6	$53.66	11.111%	$59.6222	$59.62	$59.60	$59.60
Purchase #7	$41.53	5.180%	$43.6813	$43.68	$43.70	$43.70
7 purchase totals =	$607.04		$653.7647	$653.77	$653.75	$653.80