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	$112.99	13.814%	$128.5984	$128.60	$128.60	$128.60
Purchase #2	$55.58	12.102%	$62.3063	$62.31	$62.30	$62.30
Purchase #3	$47.34	10.852%	$52.4773	$52.48	$52.50	$52.50
Purchase #4	$187.71	9.506%	$205.5537	$205.55	$205.55	$205.60
Purchase #5	$86.34	3.741%	$89.57	$89.57	$89.55	$89.60
Purchase #6	$123.25	3.313%	$127.3333	$127.33	$127.35	$127.30
Purchase #7	$135.85	5.714%	$143.6125	$143.61	$143.60	$143.60
7 purchase totals =	$749.06		$809.4515	$809.45	$809.45	$809.50