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	$106.93	10.710%	$118.3822	$118.38	$118.40	$118.40
Purchase #2	$81.42	9.425%	$89.0938	$89.09	$89.10	$89.10
Purchase #3	$125.69	7.256%	$134.8101	$134.81	$134.80	$134.80
Purchase #4	$175.50	4.453%	$183.315	$183.32	$183.30	$183.30
Purchase #5	$10.37	8.475%	$11.2489	$11.25	$11.25	$11.20
Purchase #6	$52.81	13.280%	$59.8232	$59.82	$59.80	$59.80
Purchase #7	$30.29	6.397%	$32.2277	$32.23	$32.25	$32.20
7 purchase totals =	$583.01		$628.9009	$628.90	$628.90	$628.80