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	$229.76	12.125%	$257.6184	$257.62	$257.60	$257.60
Purchase #2	$81.47	6.610%	$86.8552	$86.86	$86.85	$86.90
Purchase #3	$30.64	12.421%	$34.4458	$34.45	$34.45	$34.40
Purchase #4	$116.94	5.686%	$123.5892	$123.59	$123.60	$123.60
Purchase #5	$103.79	6.289%	$110.3174	$110.32	$110.30	$110.30
Purchase #6	$126.28	5.834%	$133.6472	$133.65	$133.65	$133.60
Purchase #7	$67.69	7.164%	$72.5393	$72.54	$72.55	$72.50
7 purchase totals =	$756.57		$819.0125	$819.03	$819.00	$818.90