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	$115.46	12.332%	$129.6985	$129.70	$129.70	$129.70
Purchase #2	$166.25	11.176%	$184.8301	$184.83	$184.85	$184.80
Purchase #3	$229.96	12.526%	$258.7648	$258.76	$258.75	$258.80
Purchase #4	$9.31	8.836%	$10.1326	$10.13	$10.15	$10.10
Purchase #5	$205.77	10.172%	$226.7009	$226.70	$226.70	$226.70
Purchase #6	$54.77	9.411%	$59.9244	$59.92	$59.90	$59.90
Purchase #7	$80.91	10.536%	$89.4347	$89.43	$89.45	$89.40
7 purchase totals =	$862.43		$959.4860	$959.47	$959.50	$959.40