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	$24.69	11.434%	$27.5131	$27.51	$27.50	$27.50
Purchase #2	$23.27	11.473%	$25.9398	$25.94	$25.95	$25.90
Purchase #3	$217.71	6.741%	$232.3858	$232.39	$232.40	$232.40
Purchase #4	$53.30	11.600%	$59.4828	$59.48	$59.50	$59.50
Purchase #5	$231.27	3.196%	$238.6614	$238.66	$238.65	$238.70
Purchase #6	$21.60	4.189%	$22.5048	$22.50	$22.50	$22.50
Purchase #7	$203.38	13.304%	$230.4377	$230.44	$230.45	$230.40
7 purchase totals =	$775.22		$836.9254	$836.92	$836.95	$836.90