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	$115.43	5.589%	$121.8814	$121.88	$121.90	$121.90
Purchase #2	$51.90	6.801%	$55.4297	$55.43	$55.45	$55.40
Purchase #3	$124.89	6.603%	$133.1365	$133.14	$133.15	$133.10
Purchase #4	$71.54	13.482%	$81.185	$81.19	$81.20	$81.20
Purchase #5	$79.67	11.782%	$89.0567	$89.06	$89.05	$89.10
Purchase #6	$49.87	7.422%	$53.5714	$53.57	$53.55	$53.60
Purchase #7	$102.89	9.130%	$112.2839	$112.28	$112.30	$112.30
7 purchase totals =	$596.19		$646.5446	$646.55	$646.60	$646.60