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	$94.69	5.515%	$99.9122	$99.91	$99.90	$99.90
Purchase #2	$59.28	10.577%	$65.55	$65.55	$65.55	$65.60
Purchase #3	$103.53	13.428%	$117.432	$117.43	$117.45	$117.40
Purchase #4	$42.80	4.149%	$44.5758	$44.58	$44.60	$44.60
Purchase #5	$21.81	7.585%	$23.4643	$23.46	$23.45	$23.50
Purchase #6	$129.43	11.239%	$143.9766	$143.98	$144.00	$144.00
Purchase #7	$57.83	7.841%	$62.3645	$62.36	$62.35	$62.40
7 purchase totals =	$509.37		$557.2754	$557.27	$557.30	$557.40