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	$43.55	5.327%	$45.8699	$45.87	$45.85	$45.90
Purchase #2	$126.49	3.464%	$130.8716	$130.87	$130.85	$130.90
Purchase #3	$132.93	9.201%	$145.1609	$145.16	$145.15	$145.20
Purchase #4	$216.62	6.613%	$230.9451	$230.95	$230.95	$230.90
Purchase #5	$18.42	13.542%	$20.9144	$20.91	$20.90	$20.90
Purchase #6	$183.88	5.705%	$194.3704	$194.37	$194.35	$194.40
Purchase #7	$66.59	8.372%	$72.1649	$72.16	$72.15	$72.20
7 purchase totals =	$788.48		$840.2972	$840.29	$840.20	$840.40