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	$57.98	10.648%	$64.1537	$64.15	$64.15	$64.20
Purchase #2	$71.62	8.685%	$77.8402	$77.84	$77.85	$77.80
Purchase #3	$75.72	6.513%	$80.6516	$80.65	$80.65	$80.70
Purchase #4	$43.30	5.837%	$45.8274	$45.83	$45.85	$45.80
Purchase #5	$48.37	13.443%	$54.8724	$54.87	$54.85	$54.90
Purchase #6	$68.87	13.255%	$77.9987	$78.00	$78.00	$78.00
Purchase #7	$99.86	11.702%	$111.5456	$111.55	$111.55	$111.50
7 purchase totals =	$465.72		$512.8896	$512.89	$512.90	$512.90