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	$111.51	11.578%	$124.4206	$124.42	$124.40	$124.40
Purchase #2	$189.98	5.183%	$199.8267	$199.83	$199.85	$199.80
Purchase #3	$191.61	13.398%	$217.2819	$217.28	$217.30	$217.30
Purchase #4	$139.60	13.235%	$158.0761	$158.08	$158.10	$158.10
Purchase #5	$212.47	6.341%	$225.9427	$225.94	$225.95	$225.90
Purchase #6	$28.50	4.582%	$29.8059	$29.81	$29.80	$29.80
Purchase #7	$78.90	5.437%	$83.1898	$83.19	$83.20	$83.20
7 purchase totals =	$952.57		$1,038.5437	$1,038.55	$1,038.60	$1,038.50