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	$138.75	3.742%	$143.942	$143.94	$143.95	$143.90
Purchase #2	$115.54	7.730%	$124.4712	$124.47	$124.45	$124.50
Purchase #3	$192.25	9.149%	$209.839	$209.84	$209.85	$209.80
Purchase #4	$207.85	12.823%	$234.5026	$234.50	$234.50	$234.50
Purchase #5	$138.85	9.346%	$151.8269	$151.83	$151.85	$151.80
Purchase #6	$69.96	12.682%	$78.8323	$78.83	$78.85	$78.80
Purchase #7	$52.96	12.189%	$59.4153	$59.42	$59.40	$59.40
7 purchase totals =	$916.16		$1,002.8293	$1,002.83	$1,002.85	$1,002.70