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	$19.59	6.292%	$20.8226	$20.82	$20.80	$20.80
Purchase #2	$72.43	7.767%	$78.0556	$78.06	$78.05	$78.10
Purchase #3	$52.59	3.413%	$54.3849	$54.38	$54.40	$54.40
Purchase #4	$188.46	4.433%	$196.8144	$196.81	$196.80	$196.80
Purchase #5	$47.85	4.448%	$49.9784	$49.98	$50.00	$50.00
Purchase #6	$79.85	4.487%	$83.4329	$83.43	$83.45	$83.40
Purchase #7	$178.62	3.469%	$184.8163	$184.82	$184.80	$184.80
7 purchase totals =	$639.39		$668.3051	$668.30	$668.30	$668.30