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	$23.28	3.225%	$24.0308	$24.03	$24.05	$24.00
Purchase #2	$123.76	12.258%	$138.9305	$138.93	$138.95	$138.90
Purchase #3	$43.66	6.622%	$46.5512	$46.55	$46.55	$46.60
Purchase #4	$105.85	10.323%	$116.7769	$116.78	$116.80	$116.80
Purchase #5	$87.92	7.432%	$94.4542	$94.45	$94.45	$94.50
Purchase #6	$29.42	9.624%	$32.2514	$32.25	$32.25	$32.30
Purchase #7	$73.83	12.243%	$82.869	$82.87	$82.85	$82.90
7 purchase totals =	$487.72		$535.8640	$535.86	$535.90	$536.00