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	$210.61	9.212%	$230.0114	$230.01	$230.00	$230.00
Purchase #2	$122.39	4.196%	$127.5255	$127.53	$127.55	$127.50
Purchase #3	$8.37	13.269%	$9.4806	$9.48	$9.50	$9.50
Purchase #4	$24.64	9.801%	$27.055	$27.06	$27.05	$27.10
Purchase #5	$69.85	9.696%	$76.6227	$76.62	$76.60	$76.60
Purchase #6	$39.29	8.127%	$42.4831	$42.48	$42.50	$42.50
Purchase #7	$144.49	10.203%	$159.2323	$159.23	$159.25	$159.20
7 purchase totals =	$619.64		$672.4106	$672.41	$672.45	$672.40