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	$247.91	10.149%	$273.0704	$273.07	$273.05	$273.10
Purchase #2	$82.94	5.671%	$87.6435	$87.64	$87.65	$87.60
Purchase #3	$121.68	4.771%	$127.4854	$127.49	$127.50	$127.50
Purchase #4	$56.42	10.298%	$62.2301	$62.23	$62.25	$62.20
Purchase #5	$101.37	10.137%	$111.6459	$111.65	$111.65	$111.60
Purchase #6	$104.46	9.609%	$114.4976	$114.50	$114.50	$114.50
Purchase #7	$174.37	12.754%	$196.6091	$196.61	$196.60	$196.60
7 purchase totals =	$889.15		$973.1820	$973.19	$973.20	$973.10