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	$56.76	4.801%	$59.485	$59.49	$59.50	$59.50
Purchase #2	$28.38	3.662%	$29.4193	$29.42	$29.40	$29.40
Purchase #3	$143.70	8.542%	$155.9749	$155.97	$155.95	$156.00
Purchase #4	$239.52	7.409%	$257.266	$257.27	$257.25	$257.30
Purchase #5	$9.47	6.869%	$10.1205	$10.12	$10.10	$10.10
Purchase #6	$83.98	7.264%	$90.0803	$90.08	$90.10	$90.10
Purchase #7	$26.33	12.109%	$29.5183	$29.52	$29.50	$29.50
7 purchase totals =	$588.14		$631.8643	$631.87	$631.80	$631.90