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	$86.80	4.257%	$90.4951	$90.50	$90.50	$90.50
Purchase #2	$134.68	4.739%	$141.0625	$141.06	$141.05	$141.10
Purchase #3	$173.49	8.268%	$187.8342	$187.83	$187.85	$187.80
Purchase #4	$205.41	13.833%	$233.8244	$233.82	$233.80	$233.80
Purchase #5	$65.46	10.701%	$72.4649	$72.46	$72.45	$72.50
Purchase #6	$246.89	3.544%	$255.6398	$255.64	$255.65	$255.60
Purchase #7	$200.49	4.659%	$209.8308	$209.83	$209.85	$209.80
7 purchase totals =	$1,113.22		$1,191.1517	$1,191.14	$1,191.15	$1,191.10