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	$227.79	12.252%	$255.6988	$255.70	$255.70	$255.70
Purchase #2	$143.26	9.149%	$156.3669	$156.37	$156.35	$156.40
Purchase #3	$48.62	9.549%	$53.2627	$53.26	$53.25	$53.30
Purchase #4	$85.93	12.754%	$96.8895	$96.89	$96.90	$96.90
Purchase #5	$120.95	5.423%	$127.5091	$127.51	$127.50	$127.50
Purchase #6	$89.92	6.206%	$95.5004	$95.50	$95.50	$95.50
Purchase #7	$112.69	7.866%	$121.5542	$121.55	$121.55	$121.60
7 purchase totals =	$829.16		$906.7816	$906.78	$906.75	$906.90