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	$61.79	7.639%	$66.5101	$66.51	$66.50	$66.50
Purchase #2	$167.73	6.476%	$178.5922	$178.59	$178.60	$178.60
Purchase #3	$86.57	12.479%	$97.3731	$97.37	$97.35	$97.40
Purchase #4	$70.55	11.252%	$78.4883	$78.49	$78.50	$78.50
Purchase #5	$56.32	13.799%	$64.0916	$64.09	$64.10	$64.10
Purchase #6	$119.70	12.111%	$134.1969	$134.20	$134.20	$134.20
Purchase #7	$61.98	7.740%	$66.7773	$66.78	$66.80	$66.80
7 purchase totals =	$624.64		$686.0295	$686.03	$686.05	$686.10