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	$56.60	12.798%	$63.8437	$63.84	$63.85	$63.80
Purchase #2	$181.37	8.462%	$196.7175	$196.72	$196.70	$196.70
Purchase #3	$52.82	7.813%	$56.9468	$56.95	$56.95	$56.90
Purchase #4	$25.89	9.774%	$28.4205	$28.42	$28.40	$28.40
Purchase #5	$21.40	12.256%	$24.0228	$24.02	$24.00	$24.00
Purchase #6	$134.63	4.749%	$141.0236	$141.02	$141.00	$141.00
Purchase #7	$145.52	9.152%	$158.838	$158.84	$158.85	$158.80
7 purchase totals =	$618.23		$669.8129	$669.81	$669.75	$669.60