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	$50.43	4.447%	$52.6726	$52.67	$52.65	$52.70
Purchase #2	$52.25	4.704%	$54.7078	$54.71	$54.70	$54.70
Purchase #3	$239.47	4.595%	$250.4736	$250.47	$250.45	$250.50
Purchase #4	$50.71	12.129%	$56.8606	$56.86	$56.85	$56.90
Purchase #5	$118.77	5.735%	$125.5815	$125.58	$125.60	$125.60
Purchase #6	$151.48	4.492%	$158.2845	$158.28	$158.30	$158.30
Purchase #7	$108.58	3.320%	$112.1849	$112.18	$112.20	$112.20
7 purchase totals =	$771.69		$810.7655	$810.75	$810.75	$810.90