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	$64.26	13.651%	$73.0321	$73.03	$73.05	$73.00
Purchase #2	$93.68	8.761%	$101.8873	$101.89	$101.90	$101.90
Purchase #3	$127.92	3.176%	$131.9827	$131.98	$132.00	$132.00
Purchase #4	$75.38	3.581%	$78.0794	$78.08	$78.10	$78.10
Purchase #5	$92.32	11.348%	$102.7965	$102.80	$102.80	$102.80
Purchase #6	$97.53	3.382%	$100.8285	$100.83	$100.85	$100.80
Purchase #7	$228.90	11.715%	$255.7156	$255.72	$255.70	$255.70
7 purchase totals =	$779.99		$844.3221	$844.33	$844.40	$844.30