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	$157.86	6.427%	$168.0057	$168.01	$168.00	$168.00
Purchase #2	$79.55	7.329%	$85.3802	$85.38	$85.40	$85.40
Purchase #3	$231.83	11.321%	$258.0755	$258.08	$258.10	$258.10
Purchase #4	$237.84	7.182%	$254.9217	$254.92	$254.90	$254.90
Purchase #5	$104.68	3.265%	$108.0978	$108.10	$108.10	$108.10
Purchase #6	$132.89	10.193%	$146.4355	$146.44	$146.45	$146.40
Purchase #7	$85.89	11.559%	$95.818	$95.82	$95.80	$95.80
7 purchase totals =	$1,030.54		$1,116.7344	$1,116.75	$1,116.75	$1,116.70