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	$36.38	11.255%	$40.4746	$40.47	$40.45	$40.50
Purchase #2	$241.59	3.250%	$249.4417	$249.44	$249.45	$249.40
Purchase #3	$54.43	13.189%	$61.6088	$61.61	$61.60	$61.60
Purchase #4	$41.28	13.856%	$46.9998	$47.00	$47.00	$47.00
Purchase #5	$172.91	13.490%	$196.2356	$196.24	$196.25	$196.20
Purchase #6	$105.42	6.465%	$112.2354	$112.24	$112.25	$112.20
Purchase #7	$11.59	7.410%	$12.4488	$12.45	$12.45	$12.40
7 purchase totals =	$663.60		$719.4447	$719.45	$719.45	$719.30