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	$154.73	10.692%	$171.2737	$171.27	$171.25	$171.30
Purchase #2	$161.73	13.401%	$183.4034	$183.40	$183.40	$183.40
Purchase #3	$122.27	8.689%	$132.894	$132.89	$132.90	$132.90
Purchase #4	$83.65	8.433%	$90.7042	$90.70	$90.70	$90.70
Purchase #5	$138.94	10.780%	$153.9177	$153.92	$153.90	$153.90
Purchase #6	$57.78	13.393%	$65.5185	$65.52	$65.50	$65.50
Purchase #7	$249.91	12.612%	$281.4286	$281.43	$281.45	$281.40
7 purchase totals =	$969.01		$1,079.1401	$1,079.13	$1,079.10	$1,079.10