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	$90.69	10.510%	$100.2215	$100.22	$100.20	$100.20
Purchase #2	$98.57	13.801%	$112.1736	$112.17	$112.15	$112.20
Purchase #3	$250.98	13.733%	$285.4471	$285.45	$285.45	$285.40
Purchase #4	$219.62	8.647%	$238.6105	$238.61	$238.60	$238.60
Purchase #5	$154.48	8.647%	$167.8379	$167.84	$167.85	$167.80
Purchase #6	$112.42	12.386%	$126.3443	$126.34	$126.35	$126.30
Purchase #7	$63.59	3.308%	$65.6936	$65.69	$65.70	$65.70
7 purchase totals =	$990.35		$1,096.3285	$1,096.32	$1,096.30	$1,096.20