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	$15.62	11.522%	$17.4197	$17.42	$17.40	$17.40
Purchase #2	$64.72	4.497%	$67.6305	$67.63	$67.65	$67.60
Purchase #3	$17.57	11.832%	$19.6489	$19.65	$19.65	$19.60
Purchase #4	$235.92	12.103%	$264.4734	$264.47	$264.45	$264.50
Purchase #5	$30.39	10.463%	$33.5697	$33.57	$33.55	$33.60
Purchase #6	$83.42	8.840%	$90.7943	$90.79	$90.80	$90.80
Purchase #7	$138.52	13.580%	$157.331	$157.33	$157.35	$157.30
7 purchase totals =	$586.16		$650.8675	$650.86	$650.85	$650.80