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	$127.87	8.631%	$138.9065	$138.91	$138.90	$138.90
Purchase #2	$85.94	13.322%	$97.3889	$97.39	$97.40	$97.40
Purchase #3	$51.92	5.170%	$54.6043	$54.60	$54.60	$54.60
Purchase #4	$238.65	11.399%	$265.8537	$265.85	$265.85	$265.90
Purchase #5	$200.68	11.781%	$224.3221	$224.32	$224.30	$224.30
Purchase #6	$197.49	12.707%	$222.5851	$222.59	$222.60	$222.60
Purchase #7	$151.92	3.253%	$156.862	$156.86	$156.85	$156.90
7 purchase totals =	$1,054.47		$1,160.5226	$1,160.52	$1,160.50	$1,160.60