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	$56.37	9.692%	$61.8334	$61.83	$61.85	$61.80
Purchase #2	$21.39	12.681%	$24.1025	$24.10	$24.10	$24.10
Purchase #3	$247.53	10.268%	$272.9464	$272.95	$272.95	$272.90
Purchase #4	$98.53	4.565%	$103.0279	$103.03	$103.05	$103.00
Purchase #5	$126.37	12.649%	$142.3545	$142.35	$142.35	$142.40
Purchase #6	$33.60	10.163%	$37.0148	$37.01	$37.00	$37.00
Purchase #7	$225.51	10.607%	$249.4298	$249.43	$249.45	$249.40
7 purchase totals =	$809.30		$890.7093	$890.70	$890.75	$890.60