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	$79.94	4.806%	$83.7819	$83.78	$83.80	$83.80
Purchase #2	$227.86	12.578%	$256.5202	$256.52	$256.50	$256.50
Purchase #3	$166.59	5.396%	$175.5792	$175.58	$175.60	$175.60
Purchase #4	$127.52	7.547%	$137.1439	$137.14	$137.15	$137.10
Purchase #5	$25.40	8.223%	$27.4886	$27.49	$27.50	$27.50
Purchase #6	$53.77	9.477%	$58.8658	$58.87	$58.85	$58.90
Purchase #7	$177.33	7.104%	$189.9275	$189.93	$189.95	$189.90
7 purchase totals =	$858.41		$929.3071	$929.31	$929.35	$929.30