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	$11.80	10.150%	$12.9977	$13.00	$13.00	$13.00
Purchase #2	$240.39	11.554%	$268.1647	$268.16	$268.15	$268.20
Purchase #3	$38.35	13.248%	$43.4306	$43.43	$43.45	$43.40
Purchase #4	$200.73	13.387%	$227.6017	$227.60	$227.60	$227.60
Purchase #5	$103.90	11.460%	$115.8069	$115.81	$115.80	$115.80
Purchase #6	$187.81	10.156%	$206.884	$206.88	$206.90	$206.90
Purchase #7	$137.92	9.553%	$151.0955	$151.10	$151.10	$151.10
7 purchase totals =	$920.90		$1,025.9811	$1,025.98	$1,026.00	$1,026.00