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	$106.75	9.496%	$116.887	$116.89	$116.90	$116.90
Purchase #2	$40.37	8.727%	$43.8931	$43.89	$43.90	$43.90
Purchase #3	$208.66	12.545%	$234.8364	$234.84	$234.85	$234.80
Purchase #4	$9.66	5.685%	$10.2092	$10.21	$10.20	$10.20
Purchase #5	$99.97	4.298%	$104.2667	$104.27	$104.25	$104.30
Purchase #6	$140.51	10.199%	$154.8406	$154.84	$154.85	$154.80
Purchase #7	$20.50	10.274%	$22.6062	$22.61	$22.60	$22.60
7 purchase totals =	$626.42		$687.5392	$687.55	$687.55	$687.50