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	$136.69	8.781%	$148.6927	$148.69	$148.70	$148.70
Purchase #2	$13.35	6.256%	$14.1852	$14.19	$14.20	$14.20
Purchase #3	$148.79	7.721%	$160.2781	$160.28	$160.30	$160.30
Purchase #4	$34.77	8.810%	$37.8332	$37.83	$37.85	$37.80
Purchase #5	$154.87	6.683%	$165.22	$165.22	$165.20	$165.20
Purchase #6	$48.55	13.460%	$55.0848	$55.08	$55.10	$55.10
Purchase #7	$81.77	9.141%	$89.2446	$89.24	$89.25	$89.20
7 purchase totals =	$618.79		$670.5386	$670.53	$670.60	$670.50