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	$16.85	12.343%	$18.9298	$18.93	$18.95	$18.90
Purchase #2	$112.41	9.510%	$123.1002	$123.10	$123.10	$123.10
Purchase #3	$69.68	11.419%	$77.6368	$77.64	$77.65	$77.60
Purchase #4	$89.94	12.292%	$100.9954	$101.00	$101.00	$101.00
Purchase #5	$201.94	6.404%	$214.8722	$214.87	$214.85	$214.90
Purchase #6	$104.75	3.611%	$108.5325	$108.53	$108.55	$108.50
Purchase #7	$160.57	6.776%	$171.4502	$171.45	$171.45	$171.50
7 purchase totals =	$756.14		$815.5171	$815.52	$815.55	$815.50