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	$75.60	9.418%	$82.72	$82.72	$82.70	$82.70
Purchase #2	$64.65	9.395%	$70.7239	$70.72	$70.70	$70.70
Purchase #3	$116.44	9.515%	$127.5193	$127.52	$127.50	$127.50
Purchase #4	$58.70	3.128%	$60.5361	$60.54	$60.55	$60.50
Purchase #5	$142.45	3.548%	$147.5041	$147.50	$147.50	$147.50
Purchase #6	$12.63	7.584%	$13.5879	$13.59	$13.60	$13.60
Purchase #7	$247.38	12.397%	$278.0477	$278.05	$278.05	$278.00
7 purchase totals =	$717.85		$780.6390	$780.64	$780.60	$780.50