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	$34.64	5.388%	$36.5064	$36.51	$36.50	$36.50
Purchase #2	$177.30	7.502%	$190.601	$190.60	$190.60	$190.60
Purchase #3	$147.78	13.707%	$168.0362	$168.04	$168.05	$168.00
Purchase #4	$12.51	10.216%	$13.788	$13.79	$13.80	$13.80
Purchase #5	$104.77	10.122%	$115.3748	$115.37	$115.35	$115.40
Purchase #6	$44.47	3.169%	$45.8793	$45.88	$45.90	$45.90
Purchase #7	$62.81	10.862%	$69.6324	$69.63	$69.65	$69.60
7 purchase totals =	$584.28		$639.8181	$639.82	$639.85	$639.80