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	$57.92	13.645%	$65.8232	$65.82	$65.80	$65.80
Purchase #2	$132.55	5.307%	$139.5844	$139.58	$139.60	$139.60
Purchase #3	$50.38	10.703%	$55.7722	$55.77	$55.75	$55.80
Purchase #4	$157.84	10.662%	$174.6689	$174.67	$174.65	$174.70
Purchase #5	$119.30	10.154%	$131.4137	$131.41	$131.40	$131.40
Purchase #6	$201.67	10.560%	$222.9664	$222.97	$222.95	$223.00
Purchase #7	$10.25	5.812%	$10.8457	$10.85	$10.85	$10.80
7 purchase totals =	$729.91		$801.0745	$801.07	$801.00	$801.10