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	$244.45	4.371%	$255.1349	$255.13	$255.15	$255.10
Purchase #2	$195.44	12.872%	$220.597	$220.60	$220.60	$220.60
Purchase #3	$84.67	6.258%	$89.9686	$89.97	$89.95	$90.00
Purchase #4	$201.27	13.245%	$227.9282	$227.93	$227.95	$227.90
Purchase #5	$139.75	13.657%	$158.8357	$158.84	$158.85	$158.80
Purchase #6	$71.52	8.863%	$77.8588	$77.86	$77.85	$77.90
Purchase #7	$17.68	12.662%	$19.9186	$19.92	$19.90	$19.90
7 purchase totals =	$954.78		$1,050.2418	$1,050.25	$1,050.25	$1,050.20