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	$81.40	11.321%	$90.6153	$90.62	$90.60	$90.60
Purchase #2	$222.61	3.813%	$231.0981	$231.10	$231.10	$231.10
Purchase #3	$12.72	4.479%	$13.2897	$13.29	$13.30	$13.30
Purchase #4	$93.45	12.166%	$104.8191	$104.82	$104.80	$104.80
Purchase #5	$36.51	5.619%	$38.5615	$38.56	$38.55	$38.60
Purchase #6	$32.87	5.125%	$34.5546	$34.55	$34.55	$34.60
Purchase #7	$152.36	12.291%	$171.0866	$171.09	$171.10	$171.10
7 purchase totals =	$631.92		$684.0249	$684.03	$684.00	$684.10