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	$128.37	12.445%	$144.3456	$144.35	$144.35	$144.30
Purchase #2	$216.55	4.139%	$225.513	$225.51	$225.50	$225.50
Purchase #3	$114.27	11.536%	$127.4522	$127.45	$127.45	$127.50
Purchase #4	$184.34	11.249%	$205.0764	$205.08	$205.10	$205.10
Purchase #5	$158.69	9.720%	$174.1147	$174.11	$174.10	$174.10
Purchase #6	$76.58	13.656%	$87.0378	$87.04	$87.05	$87.00
Purchase #7	$163.25	10.303%	$180.0696	$180.07	$180.05	$180.10
7 purchase totals =	$1,042.05		$1,143.6093	$1,143.61	$1,143.60	$1,143.60