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	$6.64	6.794%	$7.0911	$7.09	$7.10	$7.10
Purchase #2	$96.51	12.621%	$108.6905	$108.69	$108.70	$108.70
Purchase #3	$91.50	3.391%	$94.6028	$94.60	$94.60	$94.60
Purchase #4	$115.63	10.444%	$127.7064	$127.71	$127.70	$127.70
Purchase #5	$30.95	11.548%	$34.5241	$34.52	$34.50	$34.50
Purchase #6	$181.89	8.129%	$196.6758	$196.68	$196.70	$196.70
Purchase #7	$34.67	4.643%	$36.2797	$36.28	$36.30	$36.30
7 purchase totals =	$557.79		$605.5704	$605.57	$605.60	$605.60