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	$159.90	8.571%	$173.605	$173.61	$173.60	$173.60
Purchase #2	$127.60	4.138%	$132.8801	$132.88	$132.90	$132.90
Purchase #3	$31.32	3.737%	$32.4904	$32.49	$32.50	$32.50
Purchase #4	$88.91	13.194%	$100.6408	$100.64	$100.65	$100.60
Purchase #5	$134.26	5.316%	$141.3973	$141.40	$141.40	$141.40
Purchase #6	$154.82	5.292%	$163.0131	$163.01	$163.00	$163.00
Purchase #7	$139.36	4.383%	$145.4681	$145.47	$145.45	$145.50
7 purchase totals =	$836.17		$889.4948	$889.50	$889.50	$889.50