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	$33.30	10.129%	$36.673	$36.67	$36.65	$36.70
Purchase #2	$222.65	7.586%	$239.5402	$239.54	$239.55	$239.50
Purchase #3	$129.25	11.315%	$143.8746	$143.87	$143.85	$143.90
Purchase #4	$223.52	3.325%	$230.952	$230.95	$230.95	$231.00
Purchase #5	$153.59	4.381%	$160.3188	$160.32	$160.30	$160.30
Purchase #6	$78.62	13.845%	$89.5049	$89.50	$89.50	$89.50
Purchase #7	$86.54	4.224%	$90.1954	$90.20	$90.20	$90.20
7 purchase totals =	$927.47		$991.0589	$991.05	$991.00	$991.10