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	$22.56	8.251%	$24.4214	$24.42	$24.40	$24.40
Purchase #2	$114.34	11.757%	$127.783	$127.78	$127.80	$127.80
Purchase #3	$240.91	3.420%	$249.1491	$249.15	$249.15	$249.10
Purchase #4	$94.50	5.641%	$99.8307	$99.83	$99.85	$99.80
Purchase #5	$152.65	13.494%	$173.2486	$173.25	$173.25	$173.20
Purchase #6	$64.61	4.572%	$67.564	$67.56	$67.55	$67.60
Purchase #7	$115.70	10.627%	$127.9954	$128.00	$128.00	$128.00
7 purchase totals =	$805.27		$869.9922	$869.99	$870.00	$869.90