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	$199.35	11.479%	$222.2334	$222.23	$222.25	$222.20
Purchase #2	$222.83	8.291%	$241.3048	$241.30	$241.30	$241.30
Purchase #3	$100.43	5.153%	$105.6052	$105.61	$105.60	$105.60
Purchase #4	$162.75	6.156%	$172.7689	$172.77	$172.75	$172.80
Purchase #5	$43.69	9.628%	$47.8965	$47.90	$47.90	$47.90
Purchase #6	$121.40	11.753%	$135.6681	$135.67	$135.65	$135.70
Purchase #7	$56.49	13.552%	$64.1455	$64.15	$64.15	$64.10
7 purchase totals =	$906.94		$989.6224	$989.63	$989.60	$989.60