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	$37.87	3.768%	$39.2969	$39.30	$39.30	$39.30
Purchase #2	$29.40	9.767%	$32.2715	$32.27	$32.25	$32.30
Purchase #3	$114.72	10.758%	$127.0616	$127.06	$127.05	$127.10
Purchase #4	$73.50	5.494%	$77.5381	$77.54	$77.55	$77.50
Purchase #5	$244.99	4.734%	$256.5878	$256.59	$256.60	$256.60
Purchase #6	$200.25	6.840%	$213.9471	$213.95	$213.95	$213.90
Purchase #7	$118.27	4.693%	$123.8204	$123.82	$123.80	$123.80
7 purchase totals =	$819.00		$870.5234	$870.53	$870.50	$870.50