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	$99.78	8.528%	$108.2892	$108.29	$108.30	$108.30
Purchase #2	$174.43	5.789%	$184.5278	$184.53	$184.55	$184.50
Purchase #3	$150.83	12.738%	$170.0427	$170.04	$170.05	$170.00
Purchase #4	$19.77	4.144%	$20.5893	$20.59	$20.60	$20.60
Purchase #5	$86.59	4.799%	$90.7455	$90.75	$90.75	$90.70
Purchase #6	$230.65	9.478%	$252.511	$252.51	$252.50	$252.50
Purchase #7	$140.53	6.433%	$149.5703	$149.57	$149.55	$149.60
7 purchase totals =	$902.58		$976.2758	$976.28	$976.30	$976.20