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	$83.83	7.642%	$90.2363	$90.24	$90.25	$90.20
Purchase #2	$181.69	13.584%	$206.3708	$206.37	$206.35	$206.40
Purchase #3	$153.73	4.868%	$161.2136	$161.21	$161.20	$161.20
Purchase #4	$100.28	3.491%	$103.7808	$103.78	$103.80	$103.80
Purchase #5	$134.60	13.244%	$152.4264	$152.43	$152.45	$152.40
Purchase #6	$112.43	8.300%	$121.7617	$121.76	$121.75	$121.80
Purchase #7	$100.75	11.156%	$111.9897	$111.99	$112.00	$112.00
7 purchase totals =	$867.31		$947.7793	$947.78	$947.80	$947.80