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	$100.25	5.533%	$105.7968	$105.80	$105.80	$105.80
Purchase #2	$35.90	6.321%	$38.1692	$38.17	$38.15	$38.20
Purchase #3	$116.55	6.283%	$123.8728	$123.87	$123.85	$123.90
Purchase #4	$215.42	11.800%	$240.8396	$240.84	$240.85	$240.80
Purchase #5	$119.60	12.548%	$134.6074	$134.61	$134.60	$134.60
Purchase #6	$245.37	4.808%	$257.1674	$257.17	$257.15	$257.20
Purchase #7	$209.47	10.120%	$230.6684	$230.67	$230.65	$230.70
7 purchase totals =	$1,042.56		$1,131.1216	$1,131.13	$1,131.05	$1,131.20