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	$63.86	13.563%	$72.5213	$72.52	$72.50	$72.50
Purchase #2	$23.31	6.314%	$24.7818	$24.78	$24.80	$24.80
Purchase #3	$119.36	9.423%	$130.6073	$130.61	$130.60	$130.60
Purchase #4	$121.26	8.544%	$131.6205	$131.62	$131.60	$131.60
Purchase #5	$114.81	3.147%	$118.4231	$118.42	$118.40	$118.40
Purchase #6	$166.92	3.606%	$172.9391	$172.94	$172.95	$172.90
Purchase #7	$119.53	5.658%	$126.293	$126.29	$126.30	$126.30
7 purchase totals =	$729.05		$777.1861	$777.18	$777.15	$777.10