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	$157.51	5.530%	$166.2203	$166.22	$166.20	$166.20
Purchase #2	$150.60	10.526%	$166.4522	$166.45	$166.45	$166.50
Purchase #3	$75.50	6.180%	$80.1659	$80.17	$80.15	$80.20
Purchase #4	$122.97	3.521%	$127.2998	$127.30	$127.30	$127.30
Purchase #5	$148.73	12.857%	$167.8522	$167.85	$167.85	$167.90
Purchase #6	$147.90	5.211%	$155.6071	$155.61	$155.60	$155.60
Purchase #7	$129.96	3.159%	$134.0654	$134.07	$134.05	$134.10
7 purchase totals =	$933.17		$997.6629	$997.67	$997.60	$997.80