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	$72.28	8.743%	$78.5994	$78.60	$78.60	$78.60
Purchase #2	$34.34	13.768%	$39.0679	$39.07	$39.05	$39.10
Purchase #3	$54.75	10.267%	$60.3712	$60.37	$60.35	$60.40
Purchase #4	$234.99	11.318%	$261.5862	$261.59	$261.60	$261.60
Purchase #5	$137.48	10.410%	$151.7917	$151.79	$151.80	$151.80
Purchase #6	$28.63	10.195%	$31.5488	$31.55	$31.55	$31.50
Purchase #7	$135.75	9.356%	$148.4508	$148.45	$148.45	$148.50
7 purchase totals =	$698.22		$771.4160	$771.42	$771.40	$771.50