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	$100.63	10.588%	$111.2847	$111.28	$111.30	$111.30
Purchase #2	$18.49	5.796%	$19.5617	$19.56	$19.55	$19.60
Purchase #3	$11.86	7.849%	$12.7909	$12.79	$12.80	$12.80
Purchase #4	$249.85	11.819%	$279.3798	$279.38	$279.40	$279.40
Purchase #5	$179.84	10.782%	$199.2303	$199.23	$199.25	$199.20
Purchase #6	$127.25	3.616%	$131.8514	$131.85	$131.85	$131.90
Purchase #7	$61.87	5.773%	$65.4418	$65.44	$65.45	$65.40
7 purchase totals =	$749.79		$819.5406	$819.53	$819.60	$819.60