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	$45.32	13.680%	$51.5198	$51.52	$51.50	$51.50
Purchase #2	$104.27	4.429%	$108.8881	$108.89	$108.90	$108.90
Purchase #3	$171.83	8.851%	$187.0387	$187.04	$187.05	$187.00
Purchase #4	$78.79	6.431%	$83.857	$83.86	$83.85	$83.90
Purchase #5	$107.54	9.425%	$117.6756	$117.68	$117.70	$117.70
Purchase #6	$116.55	9.121%	$127.1805	$127.18	$127.20	$127.20
Purchase #7	$239.28	7.221%	$256.5584	$256.56	$256.55	$256.60
7 purchase totals =	$863.58		$932.7181	$932.73	$932.75	$932.80