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	$83.87	8.378%	$90.8966	$90.90	$90.90	$90.90
Purchase #2	$11.31	5.707%	$11.9555	$11.96	$11.95	$12.00
Purchase #3	$127.27	12.580%	$143.2806	$143.28	$143.30	$143.30
Purchase #4	$139.55	5.713%	$147.5225	$147.52	$147.50	$147.50
Purchase #5	$32.62	3.260%	$33.6834	$33.68	$33.70	$33.70
Purchase #6	$40.37	3.128%	$41.6328	$41.63	$41.65	$41.60
Purchase #7	$242.48	9.859%	$266.3861	$266.39	$266.40	$266.40
7 purchase totals =	$677.47		$735.3575	$735.36	$735.40	$735.40