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	$153.75	3.230%	$158.7161	$158.72	$158.70	$158.70
Purchase #2	$32.58	6.331%	$34.6426	$34.64	$34.65	$34.60
Purchase #3	$74.35	11.806%	$83.1278	$83.13	$83.15	$83.10
Purchase #4	$176.48	6.167%	$187.3635	$187.36	$187.35	$187.40
Purchase #5	$38.58	7.782%	$41.5823	$41.58	$41.60	$41.60
Purchase #6	$82.49	10.333%	$91.0137	$91.01	$91.00	$91.00
Purchase #7	$82.77	9.748%	$90.8384	$90.84	$90.85	$90.80
7 purchase totals =	$641.00		$687.2844	$687.28	$687.30	$687.20