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	$160.37	3.500%	$165.983	$165.98	$166.00	$166.00
Purchase #2	$5.59	3.233%	$5.7707	$5.77	$5.75	$5.80
Purchase #3	$203.68	13.189%	$230.5434	$230.54	$230.55	$230.50
Purchase #4	$210.40	13.299%	$238.3811	$238.38	$238.40	$238.40
Purchase #5	$147.47	4.711%	$154.4173	$154.42	$154.40	$154.40
Purchase #6	$155.78	7.586%	$167.5975	$167.60	$167.60	$167.60
Purchase #7	$121.33	4.791%	$127.1429	$127.14	$127.15	$127.10
7 purchase totals =	$1,004.62		$1,089.8359	$1,089.83	$1,089.85	$1,089.80