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	$107.56	8.860%	$117.0898	$117.09	$117.10	$117.10
Purchase #2	$106.82	7.174%	$114.4833	$114.48	$114.50	$114.50
Purchase #3	$236.59	13.564%	$268.6811	$268.68	$268.70	$268.70
Purchase #4	$72.84	6.578%	$77.6314	$77.63	$77.65	$77.60
Purchase #5	$144.59	3.845%	$150.1495	$150.15	$150.15	$150.10
Purchase #6	$137.31	5.262%	$144.5353	$144.54	$144.55	$144.50
Purchase #7	$99.93	11.700%	$111.6218	$111.62	$111.60	$111.60
7 purchase totals =	$905.64		$984.1922	$984.19	$984.25	$984.10