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	$70.46	10.714%	$78.0091	$78.01	$78.00	$78.00
Purchase #2	$91.70	10.409%	$101.2451	$101.25	$101.25	$101.20
Purchase #3	$77.90	3.133%	$80.3406	$80.34	$80.35	$80.30
Purchase #4	$111.54	10.406%	$123.1469	$123.15	$123.15	$123.10
Purchase #5	$12.87	13.315%	$14.5836	$14.58	$14.60	$14.60
Purchase #6	$199.42	10.493%	$220.3451	$220.35	$220.35	$220.30
Purchase #7	$24.35	3.279%	$25.1484	$25.15	$25.15	$25.10
7 purchase totals =	$588.24		$642.8188	$642.83	$642.85	$642.60