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	$239.59	10.405%	$264.5193	$264.52	$264.50	$264.50
Purchase #2	$141.86	7.504%	$152.5052	$152.51	$152.50	$152.50
Purchase #3	$123.57	8.718%	$134.3428	$134.34	$134.35	$134.30
Purchase #4	$38.70	11.546%	$43.1683	$43.17	$43.15	$43.20
Purchase #5	$148.27	9.671%	$162.6092	$162.61	$162.60	$162.60
Purchase #6	$233.85	13.525%	$265.4782	$265.48	$265.50	$265.50
Purchase #7	$161.30	5.589%	$170.3151	$170.32	$170.30	$170.30
7 purchase totals =	$1,087.14		$1,192.9381	$1,192.95	$1,192.90	$1,192.90