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	$242.68	8.583%	$263.5092	$263.51	$263.50	$263.50
Purchase #2	$249.43	12.257%	$280.0026	$280.00	$280.00	$280.00
Purchase #3	$19.58	6.562%	$20.8648	$20.86	$20.85	$20.90
Purchase #4	$230.77	12.500%	$259.6163	$259.62	$259.60	$259.60
Purchase #5	$132.99	10.112%	$146.4379	$146.44	$146.45	$146.40
Purchase #6	$14.77	11.826%	$16.5167	$16.52	$16.50	$16.50
Purchase #7	$78.59	6.223%	$83.4807	$83.48	$83.50	$83.50
7 purchase totals =	$968.81		$1,070.4282	$1,070.43	$1,070.40	$1,070.40