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	$34.45	11.106%	$38.276	$38.28	$38.30	$38.30
Purchase #2	$239.87	4.165%	$249.8606	$249.86	$249.85	$249.90
Purchase #3	$203.58	8.308%	$220.4934	$220.49	$220.50	$220.50
Purchase #4	$223.27	11.583%	$249.1314	$249.13	$249.15	$249.10
Purchase #5	$127.71	11.455%	$142.3392	$142.34	$142.35	$142.30
Purchase #6	$91.70	9.768%	$100.6573	$100.66	$100.65	$100.70
Purchase #7	$92.61	4.500%	$96.7775	$96.78	$96.80	$96.80
7 purchase totals =	$1,013.19		$1,097.5354	$1,097.54	$1,097.60	$1,097.60