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	$81.38	10.687%	$90.0771	$90.08	$90.10	$90.10
Purchase #2	$44.90	13.178%	$50.8169	$50.82	$50.80	$50.80
Purchase #3	$54.71	4.715%	$57.2896	$57.29	$57.30	$57.30
Purchase #4	$9.83	6.708%	$10.4894	$10.49	$10.50	$10.50
Purchase #5	$50.85	11.855%	$56.8783	$56.88	$56.90	$56.90
Purchase #6	$249.73	11.805%	$279.2106	$279.21	$279.20	$279.20
Purchase #7	$18.81	3.392%	$19.448	$19.45	$19.45	$19.40
7 purchase totals =	$510.21		$564.2099	$564.22	$564.25	$564.20