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	$21.46	13.781%	$24.4174	$24.42	$24.40	$24.40
Purchase #2	$198.88	3.467%	$205.7752	$205.78	$205.80	$205.80
Purchase #3	$116.65	9.376%	$127.5871	$127.59	$127.60	$127.60
Purchase #4	$154.49	4.126%	$160.8643	$160.86	$160.85	$160.90
Purchase #5	$6.88	5.643%	$7.2682	$7.27	$7.25	$7.30
Purchase #6	$59.36	10.308%	$65.4788	$65.48	$65.50	$65.50
Purchase #7	$135.50	5.216%	$142.5677	$142.57	$142.55	$142.60
7 purchase totals =	$693.22		$733.9587	$733.97	$733.95	$734.10