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	$93.37	12.749%	$105.2737	$105.27	$105.25	$105.30
Purchase #2	$60.84	10.393%	$67.1631	$67.16	$67.15	$67.20
Purchase #3	$105.27	10.341%	$116.156	$116.16	$116.15	$116.20
Purchase #4	$138.92	3.285%	$143.4835	$143.48	$143.50	$143.50
Purchase #5	$66.56	11.183%	$74.0034	$74.00	$74.00	$74.00
Purchase #6	$40.39	5.266%	$42.5169	$42.52	$42.50	$42.50
Purchase #7	$88.78	7.723%	$95.6365	$95.64	$95.65	$95.60
7 purchase totals =	$594.13		$644.2331	$644.23	$644.20	$644.30