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	$152.44	10.634%	$168.6505	$168.65	$168.65	$168.70
Purchase #2	$244.39	11.617%	$272.7808	$272.78	$272.80	$272.80
Purchase #3	$194.48	5.323%	$204.8322	$204.83	$204.85	$204.80
Purchase #4	$139.52	3.275%	$144.0893	$144.09	$144.10	$144.10
Purchase #5	$82.56	9.566%	$90.4577	$90.46	$90.45	$90.50
Purchase #6	$138.90	13.620%	$157.8182	$157.82	$157.80	$157.80
Purchase #7	$89.67	12.492%	$100.8716	$100.87	$100.85	$100.90
7 purchase totals =	$1,041.96		$1,139.5003	$1,139.50	$1,139.50	$1,139.60