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	$13.95	8.128%	$15.0839	$15.08	$15.10	$15.10
Purchase #2	$228.37	4.247%	$238.0689	$238.07	$238.05	$238.10
Purchase #3	$219.33	5.649%	$231.72	$231.72	$231.70	$231.70
Purchase #4	$113.49	11.280%	$126.2917	$126.29	$126.30	$126.30
Purchase #5	$100.89	10.582%	$111.5662	$111.57	$111.55	$111.60
Purchase #6	$149.89	13.791%	$170.5613	$170.56	$170.55	$170.60
Purchase #7	$44.38	11.103%	$49.3075	$49.31	$49.30	$49.30
7 purchase totals =	$870.30		$942.5995	$942.60	$942.55	$942.70