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	$214.55	7.862%	$231.4179	$231.42	$231.40	$231.40
Purchase #2	$65.81	7.265%	$70.5911	$70.59	$70.60	$70.60
Purchase #3	$163.55	7.314%	$175.512	$175.51	$175.50	$175.50
Purchase #4	$93.84	12.163%	$105.2538	$105.25	$105.25	$105.30
Purchase #5	$216.80	11.321%	$241.3439	$241.34	$241.35	$241.30
Purchase #6	$63.83	10.676%	$70.6445	$70.64	$70.65	$70.60
Purchase #7	$99.60	5.450%	$105.0282	$105.03	$105.05	$105.00
7 purchase totals =	$917.98		$999.7914	$999.78	$999.80	$999.70