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	$19.51	10.719%	$21.6013	$21.60	$21.60	$21.60
Purchase #2	$229.80	13.286%	$260.3312	$260.33	$260.35	$260.30
Purchase #3	$67.32	5.156%	$70.791	$70.79	$70.80	$70.80
Purchase #4	$48.96	5.341%	$51.575	$51.58	$51.60	$51.60
Purchase #5	$24.72	9.312%	$27.0219	$27.02	$27.00	$27.00
Purchase #6	$177.33	10.408%	$195.7865	$195.79	$195.80	$195.80
Purchase #7	$37.46	7.151%	$40.1388	$40.14	$40.15	$40.10
7 purchase totals =	$605.10		$667.2457	$667.25	$667.30	$667.20