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	$223.30	6.703%	$238.2678	$238.27	$238.25	$238.30
Purchase #2	$108.56	11.466%	$121.0075	$121.01	$121.00	$121.00
Purchase #3	$86.76	5.798%	$91.7903	$91.79	$91.80	$91.80
Purchase #4	$200.48	12.660%	$225.8608	$225.86	$225.85	$225.90
Purchase #5	$185.77	8.106%	$200.8285	$200.83	$200.85	$200.80
Purchase #6	$214.90	8.262%	$232.655	$232.66	$232.65	$232.70
Purchase #7	$84.80	6.114%	$89.9847	$89.98	$90.00	$90.00
7 purchase totals =	$1,104.57		$1,200.3946	$1,200.40	$1,200.40	$1,200.50