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	$46.45	13.382%	$52.6659	$52.67	$52.65	$52.70
Purchase #2	$30.71	13.549%	$34.8709	$34.87	$34.85	$34.90
Purchase #3	$85.75	8.696%	$93.2068	$93.21	$93.20	$93.20
Purchase #4	$90.42	10.311%	$99.7432	$99.74	$99.75	$99.70
Purchase #5	$81.61	10.352%	$90.0583	$90.06	$90.05	$90.10
Purchase #6	$42.34	10.481%	$46.7777	$46.78	$46.80	$46.80
Purchase #7	$187.72	12.358%	$210.9184	$210.92	$210.90	$210.90
7 purchase totals =	$565.00		$628.2412	$628.25	$628.20	$628.30