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	$20.80	4.383%	$21.7117	$21.71	$21.70	$21.70
Purchase #2	$119.55	9.650%	$131.0866	$131.09	$131.10	$131.10
Purchase #3	$53.85	3.207%	$55.577	$55.58	$55.60	$55.60
Purchase #4	$74.31	4.234%	$77.4563	$77.46	$77.45	$77.50
Purchase #5	$15.57	12.269%	$17.4803	$17.48	$17.50	$17.50
Purchase #6	$32.32	4.612%	$33.8106	$33.81	$33.80	$33.80
Purchase #7	$51.36	10.584%	$56.7959	$56.80	$56.80	$56.80
7 purchase totals =	$367.76		$393.9184	$393.93	$393.95	$394.00