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	$189.28	10.302%	$208.7796	$208.78	$208.80	$208.80
Purchase #2	$40.79	12.455%	$45.8704	$45.87	$45.85	$45.90
Purchase #3	$126.83	13.839%	$144.382	$144.38	$144.40	$144.40
Purchase #4	$231.80	5.190%	$243.8304	$243.83	$243.85	$243.80
Purchase #5	$66.88	5.324%	$70.4407	$70.44	$70.45	$70.40
Purchase #6	$109.32	12.162%	$122.6155	$122.62	$122.60	$122.60
Purchase #7	$41.85	11.457%	$46.6448	$46.64	$46.65	$46.60
7 purchase totals =	$806.75		$882.5634	$882.56	$882.60	$882.50