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	$240.37	6.724%	$256.5325	$256.53	$256.55	$256.50
Purchase #2	$229.33	6.253%	$243.67	$243.67	$243.65	$243.70
Purchase #3	$71.65	3.103%	$73.8733	$73.87	$73.85	$73.90
Purchase #4	$116.81	8.320%	$126.5286	$126.53	$126.55	$126.50
Purchase #5	$12.93	4.542%	$13.5173	$13.52	$13.50	$13.50
Purchase #6	$111.65	5.238%	$117.4982	$117.50	$117.50	$117.50
Purchase #7	$54.28	6.674%	$57.9026	$57.90	$57.90	$57.90
7 purchase totals =	$837.02		$889.5225	$889.52	$889.50	$889.50