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	$160.72	5.752%	$169.9646	$169.96	$169.95	$170.00
Purchase #2	$207.62	7.537%	$223.2683	$223.27	$223.25	$223.30
Purchase #3	$209.25	8.873%	$227.8168	$227.82	$227.80	$227.80
Purchase #4	$119.70	6.732%	$127.7582	$127.76	$127.75	$127.80
Purchase #5	$68.52	11.659%	$76.5087	$76.51	$76.50	$76.50
Purchase #6	$162.87	6.781%	$173.9142	$173.91	$173.90	$173.90
Purchase #7	$249.93	12.269%	$280.5939	$280.59	$280.60	$280.60
7 purchase totals =	$1,178.61		$1,279.8247	$1,279.82	$1,279.75	$1,279.90