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	$64.59	12.191%	$72.4642	$72.46	$72.45	$72.50
Purchase #2	$146.40	12.372%	$164.5126	$164.51	$164.50	$164.50
Purchase #3	$71.74	3.751%	$74.431	$74.43	$74.45	$74.40
Purchase #4	$227.45	11.734%	$254.139	$254.14	$254.15	$254.10
Purchase #5	$105.83	10.241%	$116.6681	$116.67	$116.65	$116.70
Purchase #6	$135.42	13.627%	$153.8737	$153.87	$153.85	$153.90
Purchase #7	$62.85	12.271%	$70.5623	$70.56	$70.55	$70.60
7 purchase totals =	$814.28		$906.6509	$906.64	$906.60	$906.70