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	$98.27	13.592%	$111.6269	$111.63	$111.65	$111.60
Purchase #2	$161.83	4.701%	$169.4376	$169.44	$169.45	$169.40
Purchase #3	$124.92	10.454%	$137.9791	$137.98	$138.00	$138.00
Purchase #4	$17.38	4.137%	$18.099	$18.10	$18.10	$18.10
Purchase #5	$214.77	12.296%	$241.1781	$241.18	$241.20	$241.20
Purchase #6	$76.43	7.413%	$82.0958	$82.10	$82.10	$82.10
Purchase #7	$202.93	10.421%	$224.0773	$224.08	$224.10	$224.10
7 purchase totals =	$896.53		$984.4938	$984.51	$984.60	$984.50