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	$31.79	3.330%	$32.8486	$32.85	$32.85	$32.80
Purchase #2	$240.79	9.179%	$262.8921	$262.89	$262.90	$262.90
Purchase #3	$69.28	12.164%	$77.7072	$77.71	$77.70	$77.70
Purchase #4	$69.32	4.712%	$72.5864	$72.59	$72.60	$72.60
Purchase #5	$15.79	10.250%	$17.4085	$17.41	$17.40	$17.40
Purchase #6	$176.72	12.115%	$198.1296	$198.13	$198.15	$198.10
Purchase #7	$134.37	7.486%	$144.4289	$144.43	$144.45	$144.40
7 purchase totals =	$738.06		$806.0013	$806.01	$806.05	$805.90