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	$71.60	12.322%	$80.4226	$80.42	$80.40	$80.40
Purchase #2	$85.55	12.463%	$96.2121	$96.21	$96.20	$96.20
Purchase #3	$190.45	13.108%	$215.4142	$215.41	$215.40	$215.40
Purchase #4	$21.56	10.337%	$23.7887	$23.79	$23.80	$23.80
Purchase #5	$123.43	3.689%	$127.9833	$127.98	$128.00	$128.00
Purchase #6	$246.84	13.747%	$280.7731	$280.77	$280.75	$280.80
Purchase #7	$180.98	4.349%	$188.8508	$188.85	$188.85	$188.90
7 purchase totals =	$920.41		$1,013.4448	$1,013.43	$1,013.40	$1,013.50