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	$224.38	13.805%	$255.3557	$255.36	$255.35	$255.40
Purchase #2	$106.43	4.352%	$111.0618	$111.06	$111.05	$111.10
Purchase #3	$56.26	8.525%	$61.0562	$61.06	$61.05	$61.10
Purchase #4	$207.75	4.847%	$217.8196	$217.82	$217.80	$217.80
Purchase #5	$145.52	5.779%	$153.9296	$153.93	$153.95	$153.90
Purchase #6	$29.46	7.531%	$31.6786	$31.68	$31.70	$31.70
Purchase #7	$226.97	13.782%	$258.251	$258.25	$258.25	$258.30
7 purchase totals =	$996.77		$1,089.1525	$1,089.16	$1,089.15	$1,089.30