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	$96.87	6.372%	$103.0426	$103.04	$103.05	$103.00
Purchase #2	$15.71	9.845%	$17.2566	$17.26	$17.25	$17.30
Purchase #3	$113.86	4.242%	$118.6899	$118.69	$118.70	$118.70
Purchase #4	$74.32	10.580%	$82.1831	$82.18	$82.20	$82.20
Purchase #5	$224.67	13.691%	$255.4296	$255.43	$255.45	$255.40
Purchase #6	$143.94	7.811%	$155.1832	$155.18	$155.20	$155.20
Purchase #7	$233.83	13.560%	$265.5373	$265.54	$265.55	$265.50
7 purchase totals =	$903.20		$997.3223	$997.32	$997.40	$997.30