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	$84.74	13.762%	$96.4019	$96.40	$96.40	$96.40
Purchase #2	$41.59	10.332%	$45.8871	$45.89	$45.90	$45.90
Purchase #3	$156.60	11.801%	$175.0804	$175.08	$175.10	$175.10
Purchase #4	$134.64	6.218%	$143.0119	$143.01	$143.00	$143.00
Purchase #5	$150.76	5.742%	$159.4166	$159.42	$159.40	$159.40
Purchase #6	$70.72	6.660%	$75.43	$75.43	$75.45	$75.40
Purchase #7	$75.38	13.178%	$85.3136	$85.31	$85.30	$85.30
7 purchase totals =	$714.43		$780.5415	$780.54	$780.55	$780.50