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	$91.64	8.489%	$99.4193	$99.42	$99.40	$99.40
Purchase #2	$204.78	4.798%	$214.6053	$214.61	$214.60	$214.60
Purchase #3	$214.42	12.577%	$241.3876	$241.39	$241.40	$241.40
Purchase #4	$38.70	9.844%	$42.5096	$42.51	$42.50	$42.50
Purchase #5	$240.33	12.864%	$271.2461	$271.25	$271.25	$271.20
Purchase #6	$52.61	3.669%	$54.5403	$54.54	$54.55	$54.50
Purchase #7	$140.34	11.226%	$156.0946	$156.09	$156.10	$156.10
7 purchase totals =	$982.82		$1,079.8028	$1,079.81	$1,079.80	$1,079.70