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	$65.86	9.814%	$72.3235	$72.32	$72.30	$72.30
Purchase #2	$218.25	6.115%	$231.596	$231.60	$231.60	$231.60
Purchase #3	$134.27	8.381%	$145.5232	$145.52	$145.50	$145.50
Purchase #4	$29.26	9.652%	$32.0842	$32.08	$32.10	$32.10
Purchase #5	$128.73	4.167%	$134.0942	$134.09	$134.10	$134.10
Purchase #6	$18.29	5.324%	$19.2638	$19.26	$19.25	$19.30
Purchase #7	$181.27	5.185%	$190.6688	$190.67	$190.65	$190.70
7 purchase totals =	$775.93		$825.5537	$825.54	$825.50	$825.60