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	$43.53	13.392%	$49.3595	$49.36	$49.35	$49.40
Purchase #2	$227.92	13.139%	$257.8664	$257.87	$257.85	$257.90
Purchase #3	$102.89	8.162%	$111.2879	$111.29	$111.30	$111.30
Purchase #4	$192.52	12.174%	$215.9574	$215.96	$215.95	$216.00
Purchase #5	$48.72	10.518%	$53.8444	$53.84	$53.85	$53.80
Purchase #6	$127.43	4.242%	$132.8356	$132.84	$132.85	$132.80
Purchase #7	$166.67	4.261%	$173.7718	$173.77	$173.75	$173.80
7 purchase totals =	$909.68		$994.9230	$994.93	$994.90	$995.00