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	$71.88	3.307%	$74.2571	$74.26	$74.25	$74.30
Purchase #2	$137.55	11.676%	$153.6103	$153.61	$153.60	$153.60
Purchase #3	$236.38	8.201%	$255.7655	$255.77	$255.75	$255.80
Purchase #4	$238.78	9.366%	$261.1441	$261.14	$261.15	$261.10
Purchase #5	$65.80	8.517%	$71.4042	$71.40	$71.40	$71.40
Purchase #6	$47.47	9.191%	$51.833	$51.83	$51.85	$51.80
Purchase #7	$116.52	9.302%	$127.3587	$127.36	$127.35	$127.40
7 purchase totals =	$914.38		$995.3729	$995.37	$995.35	$995.40