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	$63.80	13.820%	$72.6172	$72.62	$72.60	$72.60
Purchase #2	$233.86	13.755%	$266.0274	$266.03	$266.05	$266.00
Purchase #3	$97.59	5.470%	$102.9282	$102.93	$102.95	$102.90
Purchase #4	$56.90	11.367%	$63.3678	$63.37	$63.35	$63.40
Purchase #5	$31.98	6.219%	$33.9688	$33.97	$33.95	$34.00
Purchase #6	$51.85	3.789%	$53.8146	$53.81	$53.80	$53.80
Purchase #7	$64.72	10.353%	$71.4205	$71.42	$71.40	$71.40
7 purchase totals =	$600.70		$664.1445	$664.15	$664.10	$664.10