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	$34.78	12.183%	$39.0172	$39.02	$39.00	$39.00
Purchase #2	$227.58	9.611%	$249.4527	$249.45	$249.45	$249.50
Purchase #3	$47.79	3.861%	$49.6352	$49.64	$49.65	$49.60
Purchase #4	$218.83	10.856%	$242.5862	$242.59	$242.60	$242.60
Purchase #5	$243.40	11.309%	$270.9261	$270.93	$270.95	$270.90
Purchase #6	$85.72	5.536%	$90.4655	$90.47	$90.45	$90.50
Purchase #7	$188.42	11.590%	$210.2579	$210.26	$210.25	$210.30
7 purchase totals =	$1,046.52		$1,152.3408	$1,152.36	$1,152.35	$1,152.40