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	$50.94	10.406%	$56.2408	$56.24	$56.25	$56.20
Purchase #2	$241.55	6.758%	$257.8739	$257.87	$257.85	$257.90
Purchase #3	$24.98	12.459%	$28.0923	$28.09	$28.10	$28.10
Purchase #4	$137.40	7.860%	$148.1996	$148.20	$148.20	$148.20
Purchase #5	$101.32	10.432%	$111.8897	$111.89	$111.90	$111.90
Purchase #6	$111.91	4.107%	$116.5061	$116.51	$116.50	$116.50
Purchase #7	$199.72	4.585%	$208.8772	$208.88	$208.90	$208.90
7 purchase totals =	$867.82		$927.6796	$927.68	$927.70	$927.70