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	$16.91	11.339%	$18.8274	$18.83	$18.85	$18.80
Purchase #2	$198.66	6.275%	$211.1259	$211.13	$211.15	$211.10
Purchase #3	$23.56	8.587%	$25.5831	$25.58	$25.60	$25.60
Purchase #4	$100.36	8.168%	$108.5574	$108.56	$108.55	$108.60
Purchase #5	$15.92	10.395%	$17.5749	$17.57	$17.55	$17.60
Purchase #6	$130.76	6.710%	$139.534	$139.53	$139.55	$139.50
Purchase #7	$36.61	11.132%	$40.6854	$40.69	$40.70	$40.70
7 purchase totals =	$522.78		$561.8881	$561.89	$561.95	$561.90