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	$37.38	8.479%	$40.5495	$40.55	$40.55	$40.50
Purchase #2	$154.93	11.291%	$172.4231	$172.42	$172.40	$172.40
Purchase #3	$129.26	6.328%	$137.4396	$137.44	$137.45	$137.40
Purchase #4	$51.88	4.847%	$54.3946	$54.39	$54.40	$54.40
Purchase #5	$244.37	13.647%	$277.7192	$277.72	$277.70	$277.70
Purchase #6	$235.35	3.440%	$243.446	$243.45	$243.45	$243.40
Purchase #7	$44.39	6.522%	$47.2851	$47.29	$47.30	$47.30
7 purchase totals =	$897.56		$973.2571	$973.26	$973.25	$973.10