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	$134.66	7.371%	$144.5858	$144.59	$144.60	$144.60
Purchase #2	$131.88	5.612%	$139.2811	$139.28	$139.30	$139.30
Purchase #3	$127.54	8.710%	$138.6487	$138.65	$138.65	$138.60
Purchase #4	$34.35	9.341%	$37.5586	$37.56	$37.55	$37.60
Purchase #5	$136.85	7.695%	$147.3806	$147.38	$147.40	$147.40
Purchase #6	$150.26	3.685%	$155.7971	$155.80	$155.80	$155.80
Purchase #7	$71.44	7.181%	$76.5701	$76.57	$76.55	$76.60
7 purchase totals =	$786.98		$839.8220	$839.83	$839.85	$839.90