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	$81.73	8.769%	$88.8969	$88.90	$88.90	$88.90
Purchase #2	$218.75	7.211%	$234.5241	$234.52	$234.50	$234.50
Purchase #3	$13.67	13.783%	$15.5541	$15.55	$15.55	$15.60
Purchase #4	$196.83	5.854%	$208.3524	$208.35	$208.35	$208.40
Purchase #5	$164.38	9.386%	$179.8087	$179.81	$179.80	$179.80
Purchase #6	$110.40	11.571%	$123.1744	$123.17	$123.15	$123.20
Purchase #7	$123.28	7.557%	$132.5963	$132.60	$132.60	$132.60
7 purchase totals =	$909.04		$982.9069	$982.90	$982.85	$983.00