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	$105.48	13.223%	$119.4276	$119.43	$119.45	$119.40
Purchase #2	$66.84	12.124%	$74.9437	$74.94	$74.95	$74.90
Purchase #3	$215.70	3.136%	$222.4644	$222.46	$222.45	$222.50
Purchase #4	$123.94	10.794%	$137.3181	$137.32	$137.30	$137.30
Purchase #5	$61.60	10.326%	$67.9608	$67.96	$67.95	$68.00
Purchase #6	$50.81	13.549%	$57.6942	$57.69	$57.70	$57.70
Purchase #7	$54.25	4.189%	$56.5225	$56.52	$56.50	$56.50
7 purchase totals =	$678.62		$736.3313	$736.32	$736.30	$736.30