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	$127.87	9.160%	$139.5829	$139.58	$139.60	$139.60
Purchase #2	$153.83	5.584%	$162.4199	$162.42	$162.40	$162.40
Purchase #3	$141.30	12.249%	$158.6078	$158.61	$158.60	$158.60
Purchase #4	$118.70	11.106%	$131.8828	$131.88	$131.90	$131.90
Purchase #5	$163.98	5.790%	$173.4744	$173.47	$173.45	$173.50
Purchase #6	$217.33	7.381%	$233.3711	$233.37	$233.35	$233.40
Purchase #7	$175.35	3.232%	$181.0173	$181.02	$181.00	$181.00
7 purchase totals =	$1,098.36		$1,180.3562	$1,180.35	$1,180.30	$1,180.40