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	$55.56	12.271%	$62.3778	$62.38	$62.40	$62.40
Purchase #2	$111.25	10.214%	$122.6131	$122.61	$122.60	$122.60
Purchase #3	$178.43	5.253%	$187.8029	$187.80	$187.80	$187.80
Purchase #4	$43.26	11.275%	$48.1376	$48.14	$48.15	$48.10
Purchase #5	$228.29	11.847%	$255.3355	$255.34	$255.35	$255.30
Purchase #6	$114.74	7.321%	$123.1401	$123.14	$123.15	$123.10
Purchase #7	$40.26	6.212%	$42.761	$42.76	$42.75	$42.80
7 purchase totals =	$771.79		$842.1680	$842.17	$842.20	$842.10