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	$11.75	9.567%	$12.8741	$12.87	$12.85	$12.90
Purchase #2	$111.71	7.161%	$119.7096	$119.71	$119.70	$119.70
Purchase #3	$226.71	9.647%	$248.5807	$248.58	$248.60	$248.60
Purchase #4	$196.60	13.217%	$222.5846	$222.58	$222.60	$222.60
Purchase #5	$85.91	5.306%	$90.4684	$90.47	$90.45	$90.50
Purchase #6	$24.56	9.573%	$26.9111	$26.91	$26.90	$26.90
Purchase #7	$48.87	12.493%	$54.9753	$54.98	$55.00	$55.00
7 purchase totals =	$706.11		$776.1038	$776.10	$776.10	$776.20