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	$246.77	5.478%	$260.2881	$260.29	$260.30	$260.30
Purchase #2	$172.53	7.483%	$185.4404	$185.44	$185.45	$185.40
Purchase #3	$66.90	6.670%	$71.3622	$71.36	$71.35	$71.40
Purchase #4	$84.88	10.247%	$93.5777	$93.58	$93.60	$93.60
Purchase #5	$21.40	5.252%	$22.5239	$22.52	$22.50	$22.50
Purchase #6	$236.32	8.231%	$255.7715	$255.77	$255.75	$255.80
Purchase #7	$83.59	7.784%	$90.0966	$90.10	$90.10	$90.10
7 purchase totals =	$912.39		$979.0604	$979.06	$979.05	$979.10