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	$177.72	12.586%	$200.0878	$200.09	$200.10	$200.10
Purchase #2	$237.81	11.758%	$265.7717	$265.77	$265.75	$265.80
Purchase #3	$74.60	5.584%	$78.7657	$78.77	$78.75	$78.80
Purchase #4	$129.40	10.327%	$142.7631	$142.76	$142.75	$142.80
Purchase #5	$232.34	5.201%	$244.424	$244.42	$244.40	$244.40
Purchase #6	$160.60	7.128%	$172.0476	$172.05	$172.05	$172.00
Purchase #7	$166.92	11.589%	$186.2644	$186.26	$186.25	$186.30
7 purchase totals =	$1,179.39		$1,290.1243	$1,290.12	$1,290.05	$1,290.20