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	$204.76	8.155%	$221.4582	$221.46	$221.45	$221.50
Purchase #2	$221.46	12.603%	$249.3706	$249.37	$249.35	$249.40
Purchase #3	$50.90	7.770%	$54.8549	$54.85	$54.85	$54.90
Purchase #4	$46.71	3.761%	$48.4668	$48.47	$48.45	$48.50
Purchase #5	$231.79	6.526%	$246.9166	$246.92	$246.90	$246.90
Purchase #6	$80.38	11.543%	$89.6583	$89.66	$89.65	$89.70
Purchase #7	$63.50	7.792%	$68.4479	$68.45	$68.45	$68.40
7 purchase totals =	$899.50		$979.1733	$979.18	$979.10	$979.30