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	$28.31	11.680%	$31.6166	$31.62	$31.60	$31.60
Purchase #2	$191.35	13.376%	$216.945	$216.95	$216.95	$216.90
Purchase #3	$42.84	5.614%	$45.245	$45.25	$45.25	$45.20
Purchase #4	$84.34	10.202%	$92.9444	$92.94	$92.95	$92.90
Purchase #5	$241.39	10.256%	$266.147	$266.15	$266.15	$266.10
Purchase #6	$100.38	6.720%	$107.1255	$107.13	$107.15	$107.10
Purchase #7	$48.95	13.351%	$55.4853	$55.49	$55.50	$55.50
7 purchase totals =	$737.56		$815.5088	$815.53	$815.55	$815.30