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	$141.61	5.740%	$149.7384	$149.74	$149.75	$149.70
Purchase #2	$82.55	7.182%	$88.4787	$88.48	$88.50	$88.50
Purchase #3	$212.88	6.135%	$225.9402	$225.94	$225.95	$225.90
Purchase #4	$19.43	10.257%	$21.4229	$21.42	$21.40	$21.40
Purchase #5	$70.90	11.301%	$78.9124	$78.91	$78.90	$78.90
Purchase #6	$48.64	6.715%	$51.9062	$51.91	$51.90	$51.90
Purchase #7	$42.45	11.242%	$47.2222	$47.22	$47.20	$47.20
7 purchase totals =	$618.46		$663.6210	$663.62	$663.60	$663.50