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	$82.91	9.152%	$90.4979	$90.50	$90.50	$90.50
Purchase #2	$144.45	5.324%	$152.1405	$152.14	$152.15	$152.10
Purchase #3	$219.90	8.721%	$239.0775	$239.08	$239.10	$239.10
Purchase #4	$56.43	3.397%	$58.3469	$58.35	$58.35	$58.30
Purchase #5	$54.78	9.617%	$60.0482	$60.05	$60.05	$60.00
Purchase #6	$141.59	10.673%	$156.7019	$156.70	$156.70	$156.70
Purchase #7	$119.78	3.182%	$123.5914	$123.59	$123.60	$123.60
7 purchase totals =	$819.84		$880.4043	$880.41	$880.45	$880.30