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	$248.40	12.786%	$280.1604	$280.16	$280.15	$280.20
Purchase #2	$162.50	11.828%	$181.7205	$181.72	$181.70	$181.70
Purchase #3	$96.59	9.545%	$105.8095	$105.81	$105.80	$105.80
Purchase #4	$169.52	5.150%	$178.2503	$178.25	$178.25	$178.30
Purchase #5	$105.90	12.277%	$118.9013	$118.90	$118.90	$118.90
Purchase #6	$236.45	5.470%	$249.3838	$249.38	$249.40	$249.40
Purchase #7	$80.82	5.874%	$85.5674	$85.57	$85.55	$85.60
7 purchase totals =	$1,100.18		$1,199.7932	$1,199.79	$1,199.75	$1,199.90