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	$221.94	11.340%	$247.108	$247.11	$247.10	$247.10
Purchase #2	$120.52	8.809%	$131.1366	$131.14	$131.15	$131.10
Purchase #3	$246.70	13.343%	$279.6172	$279.62	$279.60	$279.60
Purchase #4	$49.54	3.536%	$51.2917	$51.29	$51.30	$51.30
Purchase #5	$108.30	7.690%	$116.6283	$116.63	$116.65	$116.60
Purchase #6	$36.30	4.177%	$37.8163	$37.82	$37.80	$37.80
Purchase #7	$78.83	13.157%	$89.2017	$89.20	$89.20	$89.20
7 purchase totals =	$862.13		$952.7998	$952.81	$952.80	$952.70