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	$39.55	9.669%	$43.3741	$43.37	$43.35	$43.40
Purchase #2	$191.72	7.709%	$206.4997	$206.50	$206.50	$206.50
Purchase #3	$241.27	10.663%	$266.9966	$267.00	$267.00	$267.00
Purchase #4	$41.37	11.443%	$46.104	$46.10	$46.10	$46.10
Purchase #5	$105.93	13.725%	$120.4689	$120.47	$120.45	$120.50
Purchase #6	$27.81	12.372%	$31.2507	$31.25	$31.25	$31.30
Purchase #7	$100.72	3.847%	$104.5947	$104.59	$104.60	$104.60
7 purchase totals =	$748.37		$819.2887	$819.28	$819.25	$819.40