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	$18.78	11.251%	$20.8929	$20.89	$20.90	$20.90
Purchase #2	$116.80	9.349%	$127.7196	$127.72	$127.70	$127.70
Purchase #3	$188.81	8.286%	$204.4548	$204.45	$204.45	$204.50
Purchase #4	$123.54	9.491%	$135.2652	$135.27	$135.25	$135.30
Purchase #5	$142.42	7.465%	$153.0517	$153.05	$153.05	$153.10
Purchase #6	$105.87	6.250%	$112.4869	$112.49	$112.50	$112.50
Purchase #7	$75.67	7.813%	$81.5821	$81.58	$81.60	$81.60
7 purchase totals =	$771.89		$835.4532	$835.45	$835.45	$835.60