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	$39.93	7.136%	$42.7794	$42.78	$42.80	$42.80
Purchase #2	$91.61	10.655%	$101.371	$101.37	$101.35	$101.40
Purchase #3	$95.46	10.672%	$105.6475	$105.65	$105.65	$105.60
Purchase #4	$100.60	8.863%	$109.5162	$109.52	$109.50	$109.50
Purchase #5	$34.84	10.443%	$38.4783	$38.48	$38.50	$38.50
Purchase #6	$208.25	6.298%	$221.3656	$221.37	$221.35	$221.40
Purchase #7	$54.91	9.332%	$60.0342	$60.03	$60.05	$60.00
7 purchase totals =	$625.60		$679.1922	$679.20	$679.20	$679.20