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	$231.51	10.841%	$256.608	$256.61	$256.60	$256.60
Purchase #2	$249.61	12.283%	$280.2696	$280.27	$280.25	$280.30
Purchase #3	$144.49	9.525%	$158.2527	$158.25	$158.25	$158.30
Purchase #4	$67.92	12.145%	$76.1689	$76.17	$76.15	$76.20
Purchase #5	$52.68	4.166%	$54.8746	$54.87	$54.85	$54.90
Purchase #6	$14.43	3.117%	$14.8798	$14.88	$14.90	$14.90
Purchase #7	$217.50	10.349%	$240.0091	$240.01	$240.00	$240.00
7 purchase totals =	$978.14		$1,081.0627	$1,081.06	$1,081.00	$1,081.20