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	$115.67	6.807%	$123.5437	$123.54	$123.55	$123.50
Purchase #2	$120.30	3.443%	$124.4419	$124.44	$124.45	$124.40
Purchase #3	$150.71	10.531%	$166.5813	$166.58	$166.60	$166.60
Purchase #4	$101.52	9.750%	$111.4182	$111.42	$111.40	$111.40
Purchase #5	$26.92	6.570%	$28.6886	$28.69	$28.70	$28.70
Purchase #6	$173.41	3.451%	$179.3944	$179.39	$179.40	$179.40
Purchase #7	$227.36	9.716%	$249.4503	$249.45	$249.45	$249.50
7 purchase totals =	$915.89		$983.5184	$983.51	$983.55	$983.50