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	$92.79	11.128%	$103.1157	$103.12	$103.10	$103.10
Purchase #2	$126.61	13.731%	$143.9948	$143.99	$144.00	$144.00
Purchase #3	$38.48	8.846%	$41.8839	$41.88	$41.90	$41.90
Purchase #4	$46.48	10.638%	$51.4245	$51.42	$51.40	$51.40
Purchase #5	$30.78	13.436%	$34.9156	$34.92	$34.90	$34.90
Purchase #6	$170.69	11.640%	$190.5583	$190.56	$190.55	$190.60
Purchase #7	$241.50	13.599%	$274.3416	$274.34	$274.35	$274.30
7 purchase totals =	$747.33		$840.2344	$840.23	$840.20	$840.20