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	$139.80	3.494%	$144.6846	$144.68	$144.70	$144.70
Purchase #2	$96.74	7.244%	$103.7478	$103.75	$103.75	$103.70
Purchase #3	$225.61	3.620%	$233.7771	$233.78	$233.80	$233.80
Purchase #4	$70.96	10.357%	$78.3093	$78.31	$78.30	$78.30
Purchase #5	$105.80	5.469%	$111.5862	$111.59	$111.60	$111.60
Purchase #6	$12.64	13.562%	$14.3542	$14.35	$14.35	$14.40
Purchase #7	$108.30	6.299%	$115.1218	$115.12	$115.10	$115.10
7 purchase totals =	$759.85		$801.5810	$801.58	$801.60	$801.60