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	$228.30	9.428%	$249.8241	$249.82	$249.80	$249.80
Purchase #2	$63.72	13.809%	$72.5191	$72.52	$72.50	$72.50
Purchase #3	$54.45	3.434%	$56.3198	$56.32	$56.30	$56.30
Purchase #4	$74.40	4.320%	$77.6141	$77.61	$77.60	$77.60
Purchase #5	$190.76	11.544%	$212.7813	$212.78	$212.80	$212.80
Purchase #6	$6.89	10.873%	$7.6391	$7.64	$7.65	$7.60
Purchase #7	$133.31	3.607%	$138.1185	$138.12	$138.10	$138.10
7 purchase totals =	$751.83		$814.8160	$814.81	$814.75	$814.70