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	$129.75	10.177%	$142.9547	$142.95	$142.95	$143.00
Purchase #2	$64.60	4.470%	$67.4876	$67.49	$67.50	$67.50
Purchase #3	$103.43	6.226%	$109.8696	$109.87	$109.85	$109.90
Purchase #4	$116.76	10.313%	$128.8015	$128.80	$128.80	$128.80
Purchase #5	$29.74	8.439%	$32.2498	$32.25	$32.25	$32.20
Purchase #6	$114.94	8.442%	$124.6432	$124.64	$124.65	$124.60
Purchase #7	$38.71	5.570%	$40.8661	$40.87	$40.85	$40.90
7 purchase totals =	$597.93		$646.8725	$646.87	$646.85	$646.90