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	$86.77	3.623%	$89.9137	$89.91	$89.90	$89.90
Purchase #2	$138.72	5.500%	$146.3496	$146.35	$146.35	$146.30
Purchase #3	$152.69	10.158%	$168.2003	$168.20	$168.20	$168.20
Purchase #4	$46.55	4.149%	$48.4814	$48.48	$48.50	$48.50
Purchase #5	$157.69	3.278%	$162.8591	$162.86	$162.85	$162.90
Purchase #6	$116.64	11.315%	$129.8378	$129.84	$129.85	$129.80
Purchase #7	$9.58	8.739%	$10.4172	$10.42	$10.40	$10.40
7 purchase totals =	$708.64		$756.0591	$756.06	$756.05	$756.00