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	$24.61	12.692%	$27.7335	$27.73	$27.75	$27.70
Purchase #2	$248.52	8.483%	$269.602	$269.60	$269.60	$269.60
Purchase #3	$31.94	6.773%	$34.1033	$34.10	$34.10	$34.10
Purchase #4	$147.94	9.807%	$162.4485	$162.45	$162.45	$162.40
Purchase #5	$166.66	4.169%	$173.6081	$173.61	$173.60	$173.60
Purchase #6	$138.47	5.786%	$146.4819	$146.48	$146.50	$146.50
Purchase #7	$69.45	3.266%	$71.7182	$71.72	$71.70	$71.70
7 purchase totals =	$827.59		$885.6955	$885.69	$885.70	$885.60