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	$121.66	5.812%	$128.7309	$128.73	$128.75	$128.70
Purchase #2	$107.42	3.298%	$110.9627	$110.96	$110.95	$111.00
Purchase #3	$45.28	13.849%	$51.5508	$51.55	$51.55	$51.60
Purchase #4	$217.33	10.459%	$240.0605	$240.06	$240.05	$240.10
Purchase #5	$117.64	8.862%	$128.0653	$128.07	$128.05	$128.10
Purchase #6	$127.72	12.556%	$143.7565	$143.76	$143.75	$143.80
Purchase #7	$75.95	3.518%	$78.6219	$78.62	$78.60	$78.60
7 purchase totals =	$813.00		$881.7486	$881.75	$881.70	$881.90