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	$228.27	5.838%	$241.5964	$241.60	$241.60	$241.60
Purchase #2	$102.49	9.719%	$112.451	$112.45	$112.45	$112.50
Purchase #3	$7.39	7.205%	$7.9224	$7.92	$7.90	$7.90
Purchase #4	$26.51	4.597%	$27.7287	$27.73	$27.75	$27.70
Purchase #5	$217.49	10.632%	$240.6135	$240.61	$240.60	$240.60
Purchase #6	$93.64	7.462%	$100.6274	$100.63	$100.65	$100.60
Purchase #7	$229.31	10.109%	$252.4909	$252.49	$252.50	$252.50
7 purchase totals =	$905.10		$983.4303	$983.43	$983.45	$983.40