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	$17.95	8.860%	$19.5404	$19.54	$19.55	$19.50
Purchase #2	$115.83	10.371%	$127.8427	$127.84	$127.85	$127.80
Purchase #3	$40.72	12.194%	$45.6854	$45.69	$45.70	$45.70
Purchase #4	$75.73	13.628%	$86.0505	$86.05	$86.05	$86.10
Purchase #5	$143.99	7.826%	$155.2587	$155.26	$155.25	$155.30
Purchase #6	$160.85	7.379%	$172.7191	$172.72	$172.70	$172.70
Purchase #7	$31.27	4.523%	$32.6843	$32.68	$32.70	$32.70
7 purchase totals =	$586.34		$639.7811	$639.78	$639.80	$639.80