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	$178.56	5.383%	$188.1719	$188.17	$188.15	$188.20
Purchase #2	$92.31	13.752%	$105.0045	$105.00	$105.00	$105.00
Purchase #3	$153.47	3.233%	$158.4317	$158.43	$158.45	$158.40
Purchase #4	$81.29	7.520%	$87.403	$87.40	$87.40	$87.40
Purchase #5	$37.42	5.335%	$39.4164	$39.42	$39.40	$39.40
Purchase #6	$169.45	11.624%	$189.1469	$189.15	$189.15	$189.10
Purchase #7	$132.85	7.744%	$143.1379	$143.14	$143.15	$143.10
7 purchase totals =	$845.35		$910.7123	$910.71	$910.70	$910.60