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	$63.94	12.684%	$72.0501	$72.05	$72.05	$72.10
Purchase #2	$100.60	7.635%	$108.2808	$108.28	$108.30	$108.30
Purchase #3	$73.83	3.600%	$76.4879	$76.49	$76.50	$76.50
Purchase #4	$69.77	11.151%	$77.5501	$77.55	$77.55	$77.60
Purchase #5	$18.50	11.392%	$20.6075	$20.61	$20.60	$20.60
Purchase #6	$166.63	7.404%	$178.9673	$178.97	$178.95	$179.00
Purchase #7	$46.95	3.434%	$48.5623	$48.56	$48.55	$48.60
7 purchase totals =	$540.22		$582.5060	$582.51	$582.50	$582.70