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	$92.69	8.382%	$100.4593	$100.46	$100.45	$100.50
Purchase #2	$192.70	6.606%	$205.4298	$205.43	$205.45	$205.40
Purchase #3	$113.38	8.837%	$123.3994	$123.40	$123.40	$123.40
Purchase #4	$47.45	5.551%	$50.0839	$50.08	$50.10	$50.10
Purchase #5	$11.74	3.395%	$12.1386	$12.14	$12.15	$12.10
Purchase #6	$55.64	7.782%	$59.9699	$59.97	$59.95	$60.00
Purchase #7	$134.95	3.323%	$139.4344	$139.43	$139.45	$139.40
7 purchase totals =	$648.55		$690.9153	$690.91	$690.95	$690.90