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	$60.50	9.220%	$66.0781	$66.08	$66.10	$66.10
Purchase #2	$18.60	13.638%	$21.1367	$21.14	$21.15	$21.10
Purchase #3	$38.33	7.632%	$41.2553	$41.26	$41.25	$41.30
Purchase #4	$139.68	8.340%	$151.3293	$151.33	$151.35	$151.30
Purchase #5	$150.76	4.864%	$158.093	$158.09	$158.10	$158.10
Purchase #6	$160.94	3.312%	$166.2703	$166.27	$166.25	$166.30
Purchase #7	$37.78	8.402%	$40.9543	$40.95	$40.95	$41.00
7 purchase totals =	$606.59		$645.1170	$645.12	$645.15	$645.20