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	$40.45	7.120%	$43.33	$43.33	$43.35	$43.30
Purchase #2	$240.87	10.774%	$266.8213	$266.82	$266.80	$266.80
Purchase #3	$49.44	7.561%	$53.1782	$53.18	$53.20	$53.20
Purchase #4	$141.27	12.225%	$158.5403	$158.54	$158.55	$158.50
Purchase #5	$104.58	10.475%	$115.5348	$115.53	$115.55	$115.50
Purchase #6	$24.84	4.105%	$25.8597	$25.86	$25.85	$25.90
Purchase #7	$49.59	11.648%	$55.3662	$55.37	$55.35	$55.40
7 purchase totals =	$651.04		$718.6305	$718.63	$718.65	$718.60