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	$90.97	9.670%	$99.7668	$99.77	$99.75	$99.80
Purchase #2	$106.88	9.765%	$117.3168	$117.32	$117.30	$117.30
Purchase #3	$143.73	10.332%	$158.5802	$158.58	$158.60	$158.60
Purchase #4	$112.96	9.660%	$123.8719	$123.87	$123.85	$123.90
Purchase #5	$34.62	3.190%	$35.7244	$35.72	$35.70	$35.70
Purchase #6	$208.99	4.649%	$218.7059	$218.71	$218.70	$218.70
Purchase #7	$99.75	9.801%	$109.5265	$109.53	$109.55	$109.50
7 purchase totals =	$797.90		$863.4925	$863.50	$863.45	$863.50