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	$37.48	4.257%	$39.0755	$39.08	$39.10	$39.10
Purchase #2	$103.30	13.153%	$116.887	$116.89	$116.90	$116.90
Purchase #3	$141.67	7.655%	$152.5148	$152.51	$152.50	$152.50
Purchase #4	$158.81	4.331%	$165.6881	$165.69	$165.70	$165.70
Purchase #5	$12.59	11.526%	$14.0411	$14.04	$14.05	$14.00
Purchase #6	$211.96	6.222%	$225.1482	$225.15	$225.15	$225.10
Purchase #7	$146.77	4.682%	$153.6418	$153.64	$153.65	$153.60
7 purchase totals =	$812.58		$866.9965	$867.00	$867.05	$866.90