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	$249.92	12.363%	$280.8176	$280.82	$280.80	$280.80
Purchase #2	$114.27	12.300%	$128.3252	$128.33	$128.35	$128.30
Purchase #3	$180.25	10.471%	$199.124	$199.12	$199.10	$199.10
Purchase #4	$89.74	12.121%	$100.6174	$100.62	$100.60	$100.60
Purchase #5	$97.27	6.245%	$103.3445	$103.34	$103.35	$103.30
Purchase #6	$11.49	4.522%	$12.0096	$12.01	$12.00	$12.00
Purchase #7	$127.25	5.653%	$134.4434	$134.44	$134.45	$134.40
7 purchase totals =	$870.19		$958.6817	$958.68	$958.65	$958.50