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	$49.54	10.551%	$54.767	$54.77	$54.75	$54.80
Purchase #2	$80.27	11.406%	$89.4256	$89.43	$89.45	$89.40
Purchase #3	$86.96	4.427%	$90.8097	$90.81	$90.80	$90.80
Purchase #4	$50.78	11.451%	$56.5948	$56.59	$56.60	$56.60
Purchase #5	$21.54	12.531%	$24.2392	$24.24	$24.25	$24.20
Purchase #6	$112.45	3.408%	$116.2823	$116.28	$116.30	$116.30
Purchase #7	$202.35	5.450%	$213.3781	$213.38	$213.40	$213.40
7 purchase totals =	$603.89		$645.4967	$645.50	$645.55	$645.50