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	$126.72	6.587%	$135.067	$135.07	$135.05	$135.10
Purchase #2	$247.45	13.218%	$280.1579	$280.16	$280.15	$280.20
Purchase #3	$235.48	10.517%	$260.2454	$260.25	$260.25	$260.20
Purchase #4	$122.68	4.189%	$127.8191	$127.82	$127.80	$127.80
Purchase #5	$132.35	11.518%	$147.5941	$147.59	$147.60	$147.60
Purchase #6	$91.35	5.382%	$96.2665	$96.27	$96.25	$96.30
Purchase #7	$89.53	3.138%	$92.3395	$92.34	$92.35	$92.30
7 purchase totals =	$1,045.56		$1,139.4895	$1,139.50	$1,139.45	$1,139.50