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	$165.87	8.445%	$179.8777	$179.88	$179.90	$179.90
Purchase #2	$115.60	10.575%	$127.8247	$127.82	$127.80	$127.80
Purchase #3	$75.60	3.414%	$78.181	$78.18	$78.20	$78.20
Purchase #4	$144.57	9.724%	$158.628	$158.63	$158.65	$158.60
Purchase #5	$83.35	4.866%	$87.4058	$87.41	$87.40	$87.40
Purchase #6	$48.63	11.549%	$54.2463	$54.25	$54.25	$54.20
Purchase #7	$16.59	10.121%	$18.2691	$18.27	$18.25	$18.30
7 purchase totals =	$650.21		$704.4326	$704.44	$704.45	$704.40