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	$184.92	7.189%	$198.2139	$198.21	$198.20	$198.20
Purchase #2	$77.55	3.116%	$79.9665	$79.97	$79.95	$80.00
Purchase #3	$144.37	9.506%	$158.0938	$158.09	$158.10	$158.10
Purchase #4	$8.89	7.160%	$9.5265	$9.53	$9.55	$9.50
Purchase #5	$17.73	6.528%	$18.8874	$18.89	$18.90	$18.90
Purchase #6	$87.57	3.787%	$90.8863	$90.89	$90.90	$90.90
Purchase #7	$122.60	4.222%	$127.7762	$127.78	$127.80	$127.80
7 purchase totals =	$643.63		$683.3506	$683.36	$683.40	$683.40