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	$15.98	9.318%	$17.469	$17.47	$17.45	$17.50
Purchase #2	$98.25	13.835%	$111.8429	$111.84	$111.85	$111.80
Purchase #3	$200.61	13.415%	$227.5218	$227.52	$227.50	$227.50
Purchase #4	$39.58	4.768%	$41.4672	$41.47	$41.45	$41.50
Purchase #5	$98.60	9.554%	$108.0202	$108.02	$108.00	$108.00
Purchase #6	$242.78	9.249%	$265.2347	$265.23	$265.25	$265.20
Purchase #7	$184.98	6.162%	$196.3785	$196.38	$196.40	$196.40
7 purchase totals =	$880.78		$967.9343	$967.93	$967.90	$967.90