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	$40.94	4.756%	$42.8871	$42.89	$42.90	$42.90
Purchase #2	$49.76	8.868%	$54.1727	$54.17	$54.15	$54.20
Purchase #3	$81.46	12.383%	$91.5472	$91.55	$91.55	$91.50
Purchase #4	$108.43	13.436%	$122.9987	$123.00	$123.00	$123.00
Purchase #5	$109.41	6.523%	$116.5468	$116.55	$116.55	$116.50
Purchase #6	$107.27	10.417%	$118.4443	$118.44	$118.45	$118.40
Purchase #7	$147.80	11.823%	$165.2744	$165.27	$165.25	$165.30
7 purchase totals =	$645.07		$711.8712	$711.87	$711.85	$711.80