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	$95.86	10.155%	$105.5946	$105.59	$105.60	$105.60
Purchase #2	$105.40	3.194%	$108.7665	$108.77	$108.75	$108.80
Purchase #3	$55.34	4.292%	$57.7152	$57.72	$57.70	$57.70
Purchase #4	$17.77	11.757%	$19.8592	$19.86	$19.85	$19.90
Purchase #5	$108.25	6.869%	$115.6857	$115.69	$115.70	$115.70
Purchase #6	$149.72	4.596%	$156.6011	$156.60	$156.60	$156.60
Purchase #7	$51.37	8.632%	$55.8043	$55.80	$55.80	$55.80
7 purchase totals =	$583.71		$620.0266	$620.03	$620.00	$620.10