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	$51.89	5.790%	$54.8944	$54.89	$54.90	$54.90
Purchase #2	$116.45	9.730%	$127.7806	$127.78	$127.80	$127.80
Purchase #3	$154.34	11.489%	$172.0721	$172.07	$172.05	$172.10
Purchase #4	$42.28	13.130%	$47.8314	$47.83	$47.85	$47.80
Purchase #5	$198.36	10.722%	$219.6282	$219.63	$219.65	$219.60
Purchase #6	$51.86	9.612%	$56.8448	$56.84	$56.85	$56.80
Purchase #7	$61.63	3.546%	$63.8154	$63.82	$63.80	$63.80
7 purchase totals =	$676.81		$742.8669	$742.86	$742.90	$742.80