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	$103.47	10.785%	$114.6292	$114.63	$114.65	$114.60
Purchase #2	$84.39	5.449%	$88.9884	$88.99	$89.00	$89.00
Purchase #3	$116.90	6.259%	$124.2168	$124.22	$124.20	$124.20
Purchase #4	$28.57	10.319%	$31.5181	$31.52	$31.50	$31.50
Purchase #5	$124.74	6.692%	$133.0876	$133.09	$133.10	$133.10
Purchase #6	$59.93	11.497%	$66.8202	$66.82	$66.80	$66.80
Purchase #7	$52.61	13.253%	$59.5824	$59.58	$59.60	$59.60
7 purchase totals =	$570.61		$618.8427	$618.85	$618.85	$618.80