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	$133.60	8.147%	$144.4844	$144.48	$144.50	$144.50
Purchase #2	$235.76	5.825%	$249.493	$249.49	$249.50	$249.50
Purchase #3	$216.56	13.384%	$245.5444	$245.54	$245.55	$245.50
Purchase #4	$111.88	3.537%	$115.8372	$115.84	$115.85	$115.80
Purchase #5	$221.85	3.449%	$229.5016	$229.50	$229.50	$229.50
Purchase #6	$127.45	10.863%	$141.2949	$141.29	$141.30	$141.30
Purchase #7	$125.88	13.660%	$143.0752	$143.08	$143.10	$143.10
7 purchase totals =	$1,172.98		$1,269.2307	$1,269.22	$1,269.30	$1,269.20