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	$170.93	3.232%	$176.4545	$176.45	$176.45	$176.50
Purchase #2	$54.92	12.654%	$61.8696	$61.87	$61.85	$61.90
Purchase #3	$213.72	9.534%	$234.0961	$234.10	$234.10	$234.10
Purchase #4	$237.52	7.694%	$255.7948	$255.79	$255.80	$255.80
Purchase #5	$19.45	8.337%	$21.0715	$21.07	$21.05	$21.10
Purchase #6	$144.32	9.665%	$158.2685	$158.27	$158.25	$158.30
Purchase #7	$169.41	6.134%	$179.8016	$179.80	$179.80	$179.80
7 purchase totals =	$1,010.27		$1,087.3566	$1,087.35	$1,087.30	$1,087.50