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	$8.57	9.715%	$9.4026	$9.40	$9.40	$9.40
Purchase #2	$172.63	8.840%	$187.8905	$187.89	$187.90	$187.90
Purchase #3	$17.35	5.412%	$18.289	$18.29	$18.30	$18.30
Purchase #4	$49.82	7.583%	$53.5979	$53.60	$53.60	$53.60
Purchase #5	$100.28	4.868%	$105.1616	$105.16	$105.15	$105.20
Purchase #6	$210.36	12.866%	$237.4249	$237.42	$237.40	$237.40
Purchase #7	$145.66	13.536%	$165.3765	$165.38	$165.40	$165.40
7 purchase totals =	$704.67		$777.1430	$777.14	$777.15	$777.20