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	$213.25	7.424%	$229.0817	$229.08	$229.10	$229.10
Purchase #2	$134.82	6.861%	$144.07	$144.07	$144.05	$144.10
Purchase #3	$34.52	11.105%	$38.3534	$38.35	$38.35	$38.40
Purchase #4	$161.92	4.278%	$168.8469	$168.85	$168.85	$168.80
Purchase #5	$60.70	9.524%	$66.4811	$66.48	$66.50	$66.50
Purchase #6	$90.62	10.825%	$100.4296	$100.43	$100.45	$100.40
Purchase #7	$46.97	7.852%	$50.6581	$50.66	$50.65	$50.70
7 purchase totals =	$742.80		$797.9208	$797.92	$797.95	$798.00