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	$225.30	13.465%	$255.6366	$255.64	$255.65	$255.60
Purchase #2	$71.60	3.810%	$74.328	$74.33	$74.35	$74.30
Purchase #3	$117.61	5.264%	$123.801	$123.80	$123.80	$123.80
Purchase #4	$42.82	13.228%	$48.4842	$48.48	$48.50	$48.50
Purchase #5	$77.30	5.393%	$81.4688	$81.47	$81.45	$81.50
Purchase #6	$6.93	8.667%	$7.5306	$7.53	$7.55	$7.50
Purchase #7	$11.77	7.713%	$12.6778	$12.68	$12.70	$12.70
7 purchase totals =	$553.33		$603.9270	$603.93	$604.00	$603.90