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	$24.95	8.794%	$27.1441	$27.14	$27.15	$27.10
Purchase #2	$47.76	11.325%	$53.1688	$53.17	$53.15	$53.20
Purchase #3	$61.28	3.546%	$63.453	$63.45	$63.45	$63.50
Purchase #4	$66.30	10.794%	$73.4564	$73.46	$73.45	$73.50
Purchase #5	$80.96	10.622%	$89.5596	$89.56	$89.55	$89.60
Purchase #6	$203.88	13.766%	$231.9461	$231.95	$231.95	$231.90
Purchase #7	$227.32	9.123%	$248.0584	$248.06	$248.05	$248.10
7 purchase totals =	$712.45		$786.7864	$786.79	$786.75	$786.90