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	$208.50	9.604%	$228.5243	$228.52	$228.50	$228.50
Purchase #2	$130.39	8.181%	$141.0572	$141.06	$141.05	$141.10
Purchase #3	$23.93	6.635%	$25.5178	$25.52	$25.50	$25.50
Purchase #4	$64.47	4.687%	$67.4917	$67.49	$67.50	$67.50
Purchase #5	$109.71	8.413%	$118.9399	$118.94	$118.95	$118.90
Purchase #6	$18.52	5.787%	$19.5918	$19.59	$19.60	$19.60
Purchase #7	$70.74	11.557%	$78.9154	$78.92	$78.90	$78.90
7 purchase totals =	$626.26		$680.0381	$680.04	$680.00	$680.00