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	$170.32	6.518%	$181.4215	$181.42	$181.40	$181.40
Purchase #2	$62.62	5.517%	$66.0747	$66.07	$66.05	$66.10
Purchase #3	$50.84	8.658%	$55.2417	$55.24	$55.25	$55.20
Purchase #4	$126.84	10.245%	$139.8348	$139.83	$139.85	$139.80
Purchase #5	$232.92	4.150%	$242.5862	$242.59	$242.60	$242.60
Purchase #6	$67.54	6.649%	$72.0307	$72.03	$72.05	$72.00
Purchase #7	$167.86	13.579%	$190.6537	$190.65	$190.65	$190.70
7 purchase totals =	$878.94		$947.8433	$947.83	$947.85	$947.80