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	$10.52	7.172%	$11.2745	$11.27	$11.25	$11.30
Purchase #2	$79.38	3.649%	$82.2766	$82.28	$82.30	$82.30
Purchase #3	$73.63	12.174%	$82.5937	$82.59	$82.60	$82.60
Purchase #4	$229.29	12.269%	$257.4216	$257.42	$257.40	$257.40
Purchase #5	$52.77	4.779%	$55.2919	$55.29	$55.30	$55.30
Purchase #6	$13.68	5.553%	$14.4397	$14.44	$14.45	$14.40
Purchase #7	$172.50	3.711%	$178.9015	$178.90	$178.90	$178.90
7 purchase totals =	$631.77		$682.1995	$682.19	$682.20	$682.20