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	$19.77	10.308%	$21.8079	$21.81	$21.80	$21.80
Purchase #2	$16.55	9.121%	$18.0595	$18.06	$18.05	$18.10
Purchase #3	$21.35	12.383%	$23.9938	$23.99	$24.00	$24.00
Purchase #4	$171.48	12.231%	$192.4537	$192.45	$192.45	$192.50
Purchase #5	$19.80	4.406%	$20.6724	$20.67	$20.65	$20.70
Purchase #6	$133.72	12.504%	$150.4403	$150.44	$150.45	$150.40
Purchase #7	$90.57	10.859%	$100.405	$100.41	$100.40	$100.40
7 purchase totals =	$473.24		$527.8326	$527.83	$527.80	$527.90