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	$223.79	7.449%	$240.4601	$240.46	$240.45	$240.50
Purchase #2	$92.45	12.755%	$104.242	$104.24	$104.25	$104.20
Purchase #3	$176.51	4.831%	$185.0372	$185.04	$185.05	$185.00
Purchase #4	$24.72	3.494%	$25.5837	$25.58	$25.60	$25.60
Purchase #5	$34.29	13.196%	$38.8149	$38.81	$38.80	$38.80
Purchase #6	$164.87	11.256%	$183.4278	$183.43	$183.45	$183.40
Purchase #7	$50.41	12.821%	$56.8731	$56.87	$56.85	$56.90
7 purchase totals =	$767.04		$834.4388	$834.43	$834.45	$834.40