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	$185.89	13.246%	$210.513	$210.51	$210.50	$210.50
Purchase #2	$118.77	4.266%	$123.8367	$123.84	$123.85	$123.80
Purchase #3	$63.92	3.303%	$66.0313	$66.03	$66.05	$66.00
Purchase #4	$55.82	9.339%	$61.033	$61.03	$61.05	$61.00
Purchase #5	$43.99	6.295%	$46.7592	$46.76	$46.75	$46.80
Purchase #6	$215.93	13.834%	$245.8018	$245.80	$245.80	$245.80
Purchase #7	$116.68	6.168%	$123.8768	$123.88	$123.90	$123.90
7 purchase totals =	$801.00		$877.8518	$877.85	$877.90	$877.80