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	$66.76	7.834%	$71.99	$71.99	$72.00	$72.00
Purchase #2	$111.28	11.316%	$123.8724	$123.87	$123.85	$123.90
Purchase #3	$207.35	9.729%	$227.5231	$227.52	$227.50	$227.50
Purchase #4	$167.88	13.391%	$190.3608	$190.36	$190.35	$190.40
Purchase #5	$74.65	5.291%	$78.5997	$78.60	$78.60	$78.60
Purchase #6	$61.58	8.490%	$66.8081	$66.81	$66.80	$66.80
Purchase #7	$240.85	3.407%	$249.0558	$249.06	$249.05	$249.10
7 purchase totals =	$930.35		$1,008.2099	$1,008.21	$1,008.15	$1,008.30