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	$237.72	12.146%	$266.5935	$266.59	$266.60	$266.60
Purchase #2	$103.55	7.777%	$111.6031	$111.60	$111.60	$111.60
Purchase #3	$80.63	7.388%	$86.5869	$86.59	$86.60	$86.60
Purchase #4	$101.67	13.409%	$115.3029	$115.30	$115.30	$115.30
Purchase #5	$144.58	5.390%	$152.3729	$152.37	$152.35	$152.40
Purchase #6	$133.97	13.679%	$152.2958	$152.30	$152.30	$152.30
Purchase #7	$249.62	6.553%	$265.9776	$265.98	$266.00	$266.00
7 purchase totals =	$1,051.74		$1,150.7327	$1,150.73	$1,150.75	$1,150.80