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	$17.92	6.322%	$19.0529	$19.05	$19.05	$19.10
Purchase #2	$53.57	12.739%	$60.3943	$60.39	$60.40	$60.40
Purchase #3	$91.72	13.186%	$103.8142	$103.81	$103.80	$103.80
Purchase #4	$144.61	9.315%	$158.0804	$158.08	$158.10	$158.10
Purchase #5	$201.89	10.365%	$222.8159	$222.82	$222.80	$222.80
Purchase #6	$176.82	8.263%	$191.4306	$191.43	$191.45	$191.40
Purchase #7	$44.87	3.304%	$46.3525	$46.35	$46.35	$46.40
7 purchase totals =	$731.40		$801.9408	$801.93	$801.95	$802.00