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	$97.42	12.178%	$109.2838	$109.28	$109.30	$109.30
Purchase #2	$43.40	13.636%	$49.318	$49.32	$49.30	$49.30
Purchase #3	$169.47	7.354%	$181.9328	$181.93	$181.95	$181.90
Purchase #4	$21.31	6.271%	$22.6464	$22.65	$22.65	$22.60
Purchase #5	$122.94	7.262%	$131.8679	$131.87	$131.85	$131.90
Purchase #6	$228.25	7.152%	$244.5744	$244.57	$244.55	$244.60
Purchase #7	$176.45	8.532%	$191.5047	$191.50	$191.50	$191.50
7 purchase totals =	$859.24		$931.1280	$931.12	$931.10	$931.10