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	$79.38	6.577%	$84.6008	$84.60	$84.60	$84.60
Purchase #2	$101.42	5.160%	$106.6533	$106.65	$106.65	$106.70
Purchase #3	$76.39	5.495%	$80.5876	$80.59	$80.60	$80.60
Purchase #4	$80.78	11.594%	$90.1456	$90.15	$90.15	$90.10
Purchase #5	$137.80	4.120%	$143.4774	$143.48	$143.50	$143.50
Purchase #6	$166.75	10.540%	$184.3255	$184.33	$184.35	$184.30
Purchase #7	$133.27	6.217%	$141.5554	$141.56	$141.55	$141.60
7 purchase totals =	$775.79		$831.3456	$831.36	$831.40	$831.40