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	$139.86	8.298%	$151.4656	$151.47	$151.45	$151.50
Purchase #2	$78.27	13.224%	$88.6204	$88.62	$88.60	$88.60
Purchase #3	$113.93	8.152%	$123.2176	$123.22	$123.20	$123.20
Purchase #4	$32.58	3.166%	$33.6115	$33.61	$33.60	$33.60
Purchase #5	$116.25	10.621%	$128.5969	$128.60	$128.60	$128.60
Purchase #6	$204.37	13.433%	$231.823	$231.82	$231.80	$231.80
Purchase #7	$207.70	12.792%	$234.269	$234.27	$234.25	$234.30
7 purchase totals =	$892.96		$991.6040	$991.61	$991.50	$991.60