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	$22.99	9.119%	$25.0865	$25.09	$25.10	$25.10
Purchase #2	$188.67	8.534%	$204.7711	$204.77	$204.75	$204.80
Purchase #3	$98.70	13.163%	$111.6919	$111.69	$111.70	$111.70
Purchase #4	$240.68	7.658%	$259.1113	$259.11	$259.10	$259.10
Purchase #5	$192.71	4.121%	$200.6516	$200.65	$200.65	$200.70
Purchase #6	$186.88	5.147%	$196.4987	$196.50	$196.50	$196.50
Purchase #7	$74.87	13.619%	$85.0665	$85.07	$85.05	$85.10
7 purchase totals =	$1,005.50		$1,082.8776	$1,082.88	$1,082.85	$1,083.00