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	$200.83	3.831%	$208.5238	$208.52	$208.50	$208.50
Purchase #2	$153.89	12.372%	$172.9293	$172.93	$172.95	$172.90
Purchase #3	$164.36	9.654%	$180.2273	$180.23	$180.25	$180.20
Purchase #4	$113.72	12.538%	$127.9782	$127.98	$128.00	$128.00
Purchase #5	$225.71	11.504%	$251.6757	$251.68	$251.70	$251.70
Purchase #6	$62.85	12.171%	$70.4995	$70.50	$70.50	$70.50
Purchase #7	$127.94	12.422%	$143.8327	$143.83	$143.85	$143.80
7 purchase totals =	$1,049.30		$1,155.6665	$1,155.67	$1,155.75	$1,155.60