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	$231.37	12.195%	$259.5856	$259.59	$259.60	$259.60
Purchase #2	$38.93	9.219%	$42.519	$42.52	$42.50	$42.50
Purchase #3	$132.85	11.798%	$148.5236	$148.52	$148.50	$148.50
Purchase #4	$13.67	10.269%	$15.0738	$15.07	$15.05	$15.10
Purchase #5	$170.47	12.642%	$192.0208	$192.02	$192.00	$192.00
Purchase #6	$106.74	9.205%	$116.5654	$116.57	$116.55	$116.60
Purchase #7	$219.81	4.468%	$229.6311	$229.63	$229.65	$229.60
7 purchase totals =	$913.84		$1,003.9193	$1,003.92	$1,003.85	$1,003.90