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	$132.32	6.255%	$140.5966	$140.60	$140.60	$140.60
Purchase #2	$74.60	3.709%	$77.3669	$77.37	$77.35	$77.40
Purchase #3	$41.87	8.608%	$45.4742	$45.47	$45.45	$45.50
Purchase #4	$117.60	3.125%	$121.275	$121.28	$121.30	$121.30
Purchase #5	$184.62	6.403%	$196.4412	$196.44	$196.45	$196.40
Purchase #6	$111.64	6.173%	$118.5315	$118.53	$118.55	$118.50
Purchase #7	$19.67	5.757%	$20.8024	$20.80	$20.80	$20.80
7 purchase totals =	$682.32		$720.4878	$720.49	$720.50	$720.50