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	$169.60	10.291%	$187.0535	$187.05	$187.05	$187.10
Purchase #2	$166.62	7.325%	$178.8249	$178.82	$178.80	$178.80
Purchase #3	$108.96	3.567%	$112.8466	$112.85	$112.85	$112.80
Purchase #4	$10.46	5.118%	$10.9953	$11.00	$11.00	$11.00
Purchase #5	$98.88	4.449%	$103.2792	$103.28	$103.30	$103.30
Purchase #6	$51.85	9.431%	$56.74	$56.74	$56.75	$56.70
Purchase #7	$34.86	7.483%	$37.4686	$37.47	$37.45	$37.50
7 purchase totals =	$641.23		$687.2081	$687.21	$687.20	$687.20