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	$138.77	8.514%	$150.5849	$150.58	$150.60	$150.60
Purchase #2	$190.34	3.701%	$197.3845	$197.38	$197.40	$197.40
Purchase #3	$22.59	8.435%	$24.4955	$24.50	$24.50	$24.50
Purchase #4	$119.31	11.825%	$133.4184	$133.42	$133.40	$133.40
Purchase #5	$18.53	11.390%	$20.6406	$20.64	$20.65	$20.60
Purchase #6	$117.94	4.352%	$123.0727	$123.07	$123.05	$123.10
Purchase #7	$114.32	7.831%	$123.2724	$123.27	$123.25	$123.30
7 purchase totals =	$721.80		$772.8690	$772.86	$772.85	$772.90