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	$42.55	13.711%	$48.384	$48.38	$48.40	$48.40
Purchase #2	$91.60	5.540%	$96.6746	$96.67	$96.65	$96.70
Purchase #3	$139.95	7.594%	$150.5778	$150.58	$150.60	$150.60
Purchase #4	$47.85	9.351%	$52.3245	$52.32	$52.30	$52.30
Purchase #5	$49.32	4.365%	$51.4728	$51.47	$51.45	$51.50
Purchase #6	$199.25	12.835%	$224.8237	$224.82	$224.80	$224.80
Purchase #7	$57.73	11.169%	$64.1779	$64.18	$64.20	$64.20
7 purchase totals =	$628.25		$688.4353	$688.42	$688.40	$688.50