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	$15.27	12.528%	$17.183	$17.18	$17.20	$17.20
Purchase #2	$111.42	10.653%	$123.2896	$123.29	$123.30	$123.30
Purchase #3	$77.96	9.594%	$85.4395	$85.44	$85.45	$85.40
Purchase #4	$192.95	8.623%	$209.5881	$209.59	$209.60	$209.60
Purchase #5	$67.95	6.514%	$72.3763	$72.38	$72.40	$72.40
Purchase #6	$140.61	8.628%	$152.7418	$152.74	$152.75	$152.70
Purchase #7	$51.52	4.768%	$53.9765	$53.98	$54.00	$54.00
7 purchase totals =	$657.68		$714.5948	$714.60	$714.70	$714.60