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	$111.67	3.463%	$115.5371	$115.54	$115.55	$115.50
Purchase #2	$194.28	10.587%	$214.8484	$214.85	$214.85	$214.80
Purchase #3	$154.29	12.656%	$173.8169	$173.82	$173.80	$173.80
Purchase #4	$78.59	11.738%	$87.8149	$87.81	$87.80	$87.80
Purchase #5	$196.58	11.553%	$219.2909	$219.29	$219.30	$219.30
Purchase #6	$171.80	8.201%	$185.8893	$185.89	$185.90	$185.90
Purchase #7	$85.71	7.552%	$92.1828	$92.18	$92.20	$92.20
7 purchase totals =	$992.92		$1,089.3803	$1,089.38	$1,089.40	$1,089.30