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	$62.86	5.434%	$66.2758	$66.28	$66.30	$66.30
Purchase #2	$87.68	8.214%	$94.882	$94.88	$94.90	$94.90
Purchase #3	$72.98	4.764%	$76.4568	$76.46	$76.45	$76.50
Purchase #4	$30.99	4.622%	$32.4224	$32.42	$32.40	$32.40
Purchase #5	$234.84	13.518%	$266.5857	$266.59	$266.60	$266.60
Purchase #6	$72.63	7.692%	$78.2167	$78.22	$78.20	$78.20
Purchase #7	$5.76	12.274%	$6.467	$6.47	$6.45	$6.50
7 purchase totals =	$567.74		$621.3064	$621.32	$621.30	$621.40