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	$29.28	6.863%	$31.2895	$31.29	$31.30	$31.30
Purchase #2	$30.85	4.828%	$32.3394	$32.34	$32.35	$32.30
Purchase #3	$215.90	13.795%	$245.6834	$245.68	$245.70	$245.70
Purchase #4	$101.71	9.336%	$111.2056	$111.21	$111.20	$111.20
Purchase #5	$138.47	10.219%	$152.6202	$152.62	$152.60	$152.60
Purchase #6	$213.62	7.858%	$230.4063	$230.41	$230.40	$230.40
Purchase #7	$159.81	9.159%	$174.447	$174.45	$174.45	$174.40
7 purchase totals =	$889.64		$977.9914	$978.00	$978.00	$977.90