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	$223.70	6.113%	$237.3748	$237.37	$237.35	$237.40
Purchase #2	$132.82	5.154%	$139.6655	$139.67	$139.65	$139.70
Purchase #3	$233.37	13.849%	$265.6894	$265.69	$265.70	$265.70
Purchase #4	$19.84	10.409%	$21.9051	$21.91	$21.90	$21.90
Purchase #5	$41.52	9.830%	$45.6014	$45.60	$45.60	$45.60
Purchase #6	$81.68	10.298%	$90.0914	$90.09	$90.10	$90.10
Purchase #7	$231.70	3.506%	$239.8234	$239.82	$239.80	$239.80
7 purchase totals =	$964.63		$1,040.1510	$1,040.15	$1,040.10	$1,040.20