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	$61.76	7.313%	$66.2765	$66.28	$66.30	$66.30
Purchase #2	$73.78	11.579%	$82.323	$82.32	$82.30	$82.30
Purchase #3	$217.88	9.379%	$238.315	$238.32	$238.30	$238.30
Purchase #4	$9.85	12.772%	$11.108	$11.11	$11.10	$11.10
Purchase #5	$30.89	3.859%	$32.082	$32.08	$32.10	$32.10
Purchase #6	$23.77	8.239%	$25.7284	$25.73	$25.75	$25.70
Purchase #7	$200.38	7.153%	$214.7132	$214.71	$214.70	$214.70
7 purchase totals =	$618.31		$670.5461	$670.55	$670.55	$670.50