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	$37.38	6.786%	$39.9166	$39.92	$39.90	$39.90
Purchase #2	$123.40	3.529%	$127.7548	$127.75	$127.75	$127.80
Purchase #3	$39.73	5.449%	$41.8949	$41.89	$41.90	$41.90
Purchase #4	$10.31	9.868%	$11.3274	$11.33	$11.35	$11.30
Purchase #5	$219.45	3.830%	$227.8549	$227.85	$227.85	$227.90
Purchase #6	$163.58	8.516%	$177.5105	$177.51	$177.50	$177.50
Purchase #7	$68.31	7.745%	$73.6006	$73.60	$73.60	$73.60
7 purchase totals =	$662.16		$699.8597	$699.85	$699.85	$699.90