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	$199.54	12.551%	$224.5843	$224.58	$224.60	$224.60
Purchase #2	$99.56	12.268%	$111.774	$111.77	$111.75	$111.80
Purchase #3	$9.78	4.713%	$10.2409	$10.24	$10.25	$10.20
Purchase #4	$41.78	10.765%	$46.2776	$46.28	$46.30	$46.30
Purchase #5	$248.67	11.620%	$277.5655	$277.57	$277.55	$277.60
Purchase #6	$241.85	5.465%	$255.0671	$255.07	$255.05	$255.10
Purchase #7	$108.47	8.389%	$117.5695	$117.57	$117.55	$117.60
7 purchase totals =	$949.65		$1,043.0789	$1,043.08	$1,043.05	$1,043.20