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	$221.61	12.466%	$249.2359	$249.24	$249.25	$249.20
Purchase #2	$180.88	8.644%	$196.5153	$196.52	$196.50	$196.50
Purchase #3	$99.39	12.363%	$111.6776	$111.68	$111.70	$111.70
Purchase #4	$156.67	5.159%	$164.7526	$164.75	$164.75	$164.80
Purchase #5	$127.47	9.714%	$139.8524	$139.85	$139.85	$139.90
Purchase #6	$205.33	4.687%	$214.9538	$214.95	$214.95	$215.00
Purchase #7	$52.62	12.137%	$59.0065	$59.01	$59.00	$59.00
7 purchase totals =	$1,043.97		$1,135.9941	$1,136.00	$1,136.00	$1,136.10