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	$81.33	10.259%	$89.6736	$89.67	$89.65	$89.70
Purchase #2	$142.94	3.776%	$148.3374	$148.34	$148.35	$148.30
Purchase #3	$108.33	10.350%	$119.5422	$119.54	$119.55	$119.50
Purchase #4	$180.68	5.245%	$190.1567	$190.16	$190.15	$190.20
Purchase #5	$144.40	6.233%	$153.4005	$153.40	$153.40	$153.40
Purchase #6	$38.86	13.296%	$44.0268	$44.03	$44.05	$44.00
Purchase #7	$144.62	10.813%	$160.2578	$160.26	$160.25	$160.30
7 purchase totals =	$841.16		$905.3950	$905.40	$905.40	$905.40