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	$100.39	3.462%	$103.8655	$103.87	$103.85	$103.90
Purchase #2	$184.37	12.483%	$207.3849	$207.38	$207.40	$207.40
Purchase #3	$97.94	11.341%	$109.0474	$109.05	$109.05	$109.00
Purchase #4	$37.90	9.420%	$41.4702	$41.47	$41.45	$41.50
Purchase #5	$12.31	10.516%	$13.6045	$13.60	$13.60	$13.60
Purchase #6	$242.56	3.805%	$251.7894	$251.79	$251.80	$251.80
Purchase #7	$100.58	10.624%	$111.2656	$111.27	$111.25	$111.30
7 purchase totals =	$776.05		$838.4275	$838.43	$838.40	$838.50