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	$85.91	4.143%	$89.4693	$89.47	$89.45	$89.50
Purchase #2	$172.63	9.189%	$188.493	$188.49	$188.50	$188.50
Purchase #3	$20.29	7.628%	$21.8377	$21.84	$21.85	$21.80
Purchase #4	$110.91	4.420%	$115.8122	$115.81	$115.80	$115.80
Purchase #5	$154.82	7.267%	$166.0708	$166.07	$166.05	$166.10
Purchase #6	$240.62	6.248%	$255.6539	$255.65	$255.65	$255.70
Purchase #7	$50.27	4.233%	$52.3979	$52.40	$52.40	$52.40
7 purchase totals =	$835.45		$889.7348	$889.73	$889.70	$889.80