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	$24.50	11.103%	$27.2202	$27.22	$27.20	$27.20
Purchase #2	$56.48	5.637%	$59.6638	$59.66	$59.65	$59.70
Purchase #3	$107.51	10.297%	$118.5803	$118.58	$118.60	$118.60
Purchase #4	$232.95	9.204%	$254.3907	$254.39	$254.40	$254.40
Purchase #5	$114.77	11.383%	$127.8343	$127.83	$127.85	$127.80
Purchase #6	$119.27	3.388%	$123.3109	$123.31	$123.30	$123.30
Purchase #7	$226.38	13.372%	$256.6515	$256.65	$256.65	$256.70
7 purchase totals =	$881.86		$967.6517	$967.64	$967.65	$967.70