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	$8.28	8.611%	$8.993	$8.99	$9.00	$9.00
Purchase #2	$93.80	8.444%	$101.7205	$101.72	$101.70	$101.70
Purchase #3	$68.92	5.812%	$72.9256	$72.93	$72.95	$72.90
Purchase #4	$122.66	6.501%	$130.6341	$130.63	$130.65	$130.60
Purchase #5	$232.71	11.105%	$258.5524	$258.55	$258.55	$258.60
Purchase #6	$173.41	8.677%	$188.4568	$188.46	$188.45	$188.50
Purchase #7	$242.27	5.271%	$255.0401	$255.04	$255.05	$255.00
7 purchase totals =	$942.05		$1,016.3225	$1,016.32	$1,016.35	$1,016.30