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	$29.94	13.194%	$33.8903	$33.89	$33.90	$33.90
Purchase #2	$9.80	11.419%	$10.9191	$10.92	$10.90	$10.90
Purchase #3	$16.25	4.626%	$17.0017	$17.00	$17.00	$17.00
Purchase #4	$123.29	11.820%	$137.8629	$137.86	$137.85	$137.90
Purchase #5	$103.68	12.692%	$116.8391	$116.84	$116.85	$116.80
Purchase #6	$104.35	12.407%	$117.2967	$117.30	$117.30	$117.30
Purchase #7	$84.60	8.102%	$91.4543	$91.45	$91.45	$91.50
7 purchase totals =	$471.91		$525.2641	$525.26	$525.25	$525.30