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	$234.86	9.307%	$256.7184	$256.72	$256.70	$256.70
Purchase #2	$101.58	10.764%	$112.5141	$112.51	$112.50	$112.50
Purchase #3	$92.86	8.557%	$100.806	$100.81	$100.80	$100.80
Purchase #4	$246.25	6.454%	$262.143	$262.14	$262.15	$262.10
Purchase #5	$204.81	10.515%	$226.3458	$226.35	$226.35	$226.30
Purchase #6	$51.79	3.237%	$53.4664	$53.47	$53.45	$53.50
Purchase #7	$134.94	5.426%	$142.2618	$142.26	$142.25	$142.30
7 purchase totals =	$1,067.09		$1,154.2555	$1,154.26	$1,154.20	$1,154.20