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	$162.43	10.315%	$179.1847	$179.18	$179.20	$179.20
Purchase #2	$139.59	6.158%	$148.186	$148.19	$148.20	$148.20
Purchase #3	$249.36	12.393%	$280.2632	$280.26	$280.25	$280.30
Purchase #4	$153.37	11.145%	$170.4631	$170.46	$170.45	$170.50
Purchase #5	$51.48	8.163%	$55.6823	$55.68	$55.70	$55.70
Purchase #6	$75.67	3.610%	$78.4017	$78.40	$78.40	$78.40
Purchase #7	$172.52	8.169%	$186.6132	$186.61	$186.60	$186.60
7 purchase totals =	$1,004.42		$1,098.7942	$1,098.78	$1,098.80	$1,098.90