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	$32.55	8.762%	$35.402	$35.40	$35.40	$35.40
Purchase #2	$78.75	13.685%	$89.5269	$89.53	$89.55	$89.50
Purchase #3	$129.28	12.864%	$145.9106	$145.91	$145.90	$145.90
Purchase #4	$8.25	12.487%	$9.2802	$9.28	$9.30	$9.30
Purchase #5	$109.57	7.324%	$117.5949	$117.59	$117.60	$117.60
Purchase #6	$89.75	7.236%	$96.2443	$96.24	$96.25	$96.20
Purchase #7	$158.62	4.721%	$166.1085	$166.11	$166.10	$166.10
7 purchase totals =	$606.77		$660.0674	$660.06	$660.10	$660.00