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	$71.45	9.519%	$78.2513	$78.25	$78.25	$78.30
Purchase #2	$13.87	7.205%	$14.8693	$14.87	$14.85	$14.90
Purchase #3	$192.78	11.290%	$214.5449	$214.54	$214.55	$214.50
Purchase #4	$65.30	9.202%	$71.3089	$71.31	$71.30	$71.30
Purchase #5	$179.53	5.702%	$189.7668	$189.77	$189.75	$189.80
Purchase #6	$201.25	8.321%	$217.996	$218.00	$218.00	$218.00
Purchase #7	$184.49	4.146%	$192.139	$192.14	$192.15	$192.10
7 purchase totals =	$908.67		$978.8762	$978.88	$978.85	$978.90