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	$122.86	6.160%	$130.4282	$130.43	$130.45	$130.40
Purchase #2	$88.63	5.802%	$93.7723	$93.77	$93.75	$93.80
Purchase #3	$168.77	10.123%	$185.8546	$185.85	$185.85	$185.90
Purchase #4	$130.76	10.671%	$144.7134	$144.71	$144.70	$144.70
Purchase #5	$237.83	7.491%	$255.6458	$255.65	$255.65	$255.60
Purchase #6	$155.61	10.805%	$172.4237	$172.42	$172.40	$172.40
Purchase #7	$95.84	10.571%	$105.9712	$105.97	$105.95	$106.00
7 purchase totals =	$1,000.30		$1,088.8092	$1,088.80	$1,088.75	$1,088.80