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	$49.33	11.230%	$54.8698	$54.87	$54.85	$54.90
Purchase #2	$92.64	13.509%	$105.1547	$105.15	$105.15	$105.20
Purchase #3	$178.51	6.778%	$190.6094	$190.61	$190.60	$190.60
Purchase #4	$131.87	3.552%	$136.554	$136.55	$136.55	$136.60
Purchase #5	$22.54	13.610%	$25.6077	$25.61	$25.60	$25.60
Purchase #6	$115.44	6.667%	$123.1364	$123.14	$123.15	$123.10
Purchase #7	$114.55	4.538%	$119.7483	$119.75	$119.75	$119.70
7 purchase totals =	$704.88		$755.6803	$755.68	$755.65	$755.70