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	$67.78	6.513%	$72.1945	$72.19	$72.20	$72.20
Purchase #2	$127.34	13.164%	$144.103	$144.10	$144.10	$144.10
Purchase #3	$142.72	8.862%	$155.3678	$155.37	$155.35	$155.40
Purchase #4	$148.41	13.286%	$168.1278	$168.13	$168.15	$168.10
Purchase #5	$11.87	5.746%	$12.5521	$12.55	$12.55	$12.60
Purchase #6	$81.35	5.483%	$85.8104	$85.81	$85.80	$85.80
Purchase #7	$134.59	10.159%	$148.263	$148.26	$148.25	$148.30
7 purchase totals =	$714.06		$786.4186	$786.41	$786.40	$786.50