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	$115.27	5.738%	$121.8842	$121.88	$121.90	$121.90
Purchase #2	$119.88	6.668%	$127.8736	$127.87	$127.85	$127.90
Purchase #3	$11.51	11.495%	$12.8331	$12.83	$12.85	$12.80
Purchase #4	$35.27	6.657%	$37.6179	$37.62	$37.60	$37.60
Purchase #5	$53.49	5.162%	$56.2512	$56.25	$56.25	$56.30
Purchase #6	$84.49	8.833%	$91.953	$91.95	$91.95	$92.00
Purchase #7	$97.35	8.683%	$105.8029	$105.80	$105.80	$105.80
7 purchase totals =	$517.26		$554.2159	$554.20	$554.20	$554.30