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	$97.66	6.304%	$103.8165	$103.82	$103.80	$103.80
Purchase #2	$129.41	6.397%	$137.6884	$137.69	$137.70	$137.70
Purchase #3	$217.45	6.510%	$231.606	$231.61	$231.60	$231.60
Purchase #4	$33.87	13.128%	$38.3165	$38.32	$38.30	$38.30
Purchase #5	$39.34	3.319%	$40.6457	$40.65	$40.65	$40.60
Purchase #6	$227.62	9.563%	$249.3873	$249.39	$249.40	$249.40
Purchase #7	$39.80	5.808%	$42.1116	$42.11	$42.10	$42.10
7 purchase totals =	$785.15		$843.5720	$843.59	$843.55	$843.50