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	$22.89	11.771%	$25.5844	$25.58	$25.60	$25.60
Purchase #2	$228.95	5.103%	$240.6333	$240.63	$240.65	$240.60
Purchase #3	$214.27	3.701%	$222.2001	$222.20	$222.20	$222.20
Purchase #4	$140.45	13.556%	$159.4894	$159.49	$159.50	$159.50
Purchase #5	$116.96	8.566%	$126.9788	$126.98	$127.00	$127.00
Purchase #6	$145.76	3.793%	$151.2887	$151.29	$151.30	$151.30
Purchase #7	$106.32	12.483%	$119.5919	$119.59	$119.60	$119.60
7 purchase totals =	$975.60		$1,045.7666	$1,045.76	$1,045.85	$1,045.80