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	$221.40	9.548%	$242.5393	$242.54	$242.55	$242.50
Purchase #2	$54.83	6.651%	$58.4767	$58.48	$58.50	$58.50
Purchase #3	$102.80	13.267%	$116.4385	$116.44	$116.45	$116.40
Purchase #4	$63.75	13.791%	$72.5418	$72.54	$72.55	$72.50
Purchase #5	$16.97	5.463%	$17.8971	$17.90	$17.90	$17.90
Purchase #6	$104.53	7.634%	$112.5098	$112.51	$112.50	$112.50
Purchase #7	$249.50	11.494%	$278.1775	$278.18	$278.20	$278.20
7 purchase totals =	$813.78		$898.5807	$898.59	$898.65	$898.50