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	$127.50	12.600%	$143.565	$143.57	$143.55	$143.60
Purchase #2	$250.98	13.586%	$285.0781	$285.08	$285.10	$285.10
Purchase #3	$202.45	11.229%	$225.1831	$225.18	$225.20	$225.20
Purchase #4	$186.61	10.339%	$205.9036	$205.90	$205.90	$205.90
Purchase #5	$101.57	4.224%	$105.8603	$105.86	$105.85	$105.90
Purchase #6	$32.60	6.787%	$34.8126	$34.81	$34.80	$34.80
Purchase #7	$206.86	12.773%	$233.2822	$233.28	$233.30	$233.30
7 purchase totals =	$1,108.57		$1,233.6849	$1,233.68	$1,233.70	$1,233.80