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	$11.58	6.521%	$12.3351	$12.34	$12.35	$12.30
Purchase #2	$232.47	8.326%	$251.8255	$251.83	$251.85	$251.80
Purchase #3	$217.33	9.413%	$237.7873	$237.79	$237.80	$237.80
Purchase #4	$163.67	5.578%	$172.7995	$172.80	$172.80	$172.80
Purchase #5	$113.85	8.168%	$123.1493	$123.15	$123.15	$123.10
Purchase #6	$171.86	6.199%	$182.5136	$182.51	$182.50	$182.50
Purchase #7	$165.46	4.340%	$172.641	$172.64	$172.65	$172.60
7 purchase totals =	$1,076.22		$1,153.0513	$1,153.06	$1,153.10	$1,152.90