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	$89.48	6.686%	$95.4626	$95.46	$95.45	$95.50
Purchase #2	$94.46	11.712%	$105.5232	$105.52	$105.50	$105.50
Purchase #3	$185.91	10.112%	$204.7092	$204.71	$204.70	$204.70
Purchase #4	$21.55	6.653%	$22.9837	$22.98	$23.00	$23.00
Purchase #5	$69.80	10.108%	$76.8554	$76.86	$76.85	$76.90
Purchase #6	$104.34	7.268%	$111.9234	$111.92	$111.90	$111.90
Purchase #7	$29.42	10.328%	$32.4585	$32.46	$32.45	$32.50
7 purchase totals =	$594.96		$649.9160	$649.91	$649.85	$650.00