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	$88.89	13.308%	$100.7195	$100.72	$100.70	$100.70
Purchase #2	$129.72	7.617%	$139.6008	$139.60	$139.60	$139.60
Purchase #3	$61.86	11.183%	$68.7778	$68.78	$68.80	$68.80
Purchase #4	$31.98	13.720%	$36.3677	$36.37	$36.35	$36.40
Purchase #5	$105.38	12.435%	$118.484	$118.48	$118.50	$118.50
Purchase #6	$44.67	13.448%	$50.6772	$50.68	$50.70	$50.70
Purchase #7	$46.31	8.379%	$50.1903	$50.19	$50.20	$50.20
7 purchase totals =	$508.81		$564.8173	$564.82	$564.85	$564.90