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	$12.98	6.351%	$13.8044	$13.80	$13.80	$13.80
Purchase #2	$120.59	6.528%	$128.4621	$128.46	$128.45	$128.50
Purchase #3	$96.52	8.668%	$104.8864	$104.89	$104.90	$104.90
Purchase #4	$120.93	5.383%	$127.4397	$127.44	$127.45	$127.40
Purchase #5	$176.50	7.724%	$190.1329	$190.13	$190.15	$190.10
Purchase #6	$137.62	4.454%	$143.7496	$143.75	$143.75	$143.70
Purchase #7	$124.33	7.249%	$133.3427	$133.34	$133.35	$133.30
7 purchase totals =	$789.47		$841.8178	$841.81	$841.85	$841.70