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	$248.34	12.643%	$279.7376	$279.74	$279.75	$279.70
Purchase #2	$236.35	8.236%	$255.8158	$255.82	$255.80	$255.80
Purchase #3	$100.44	5.410%	$105.8738	$105.87	$105.85	$105.90
Purchase #4	$152.52	6.222%	$162.0098	$162.01	$162.00	$162.00
Purchase #5	$150.28	6.432%	$159.946	$159.95	$159.95	$159.90
Purchase #6	$244.68	12.190%	$274.5065	$274.51	$274.50	$274.50
Purchase #7	$30.75	9.294%	$33.6079	$33.61	$33.60	$33.60
7 purchase totals =	$1,163.36		$1,271.4974	$1,271.51	$1,271.45	$1,271.40