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	$39.57	8.632%	$42.9857	$42.99	$43.00	$43.00
Purchase #2	$164.38	4.287%	$171.427	$171.43	$171.45	$171.40
Purchase #3	$91.96	11.472%	$102.5097	$102.51	$102.50	$102.50
Purchase #4	$27.72	3.135%	$28.589	$28.59	$28.60	$28.60
Purchase #5	$23.61	3.788%	$24.5043	$24.50	$24.50	$24.50
Purchase #6	$139.27	12.194%	$156.2526	$156.25	$156.25	$156.30
Purchase #7	$235.85	5.188%	$248.0859	$248.09	$248.10	$248.10
7 purchase totals =	$722.36		$774.3542	$774.36	$774.40	$774.40