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	$241.68	13.123%	$273.3957	$273.40	$273.40	$273.40
Purchase #2	$137.98	9.476%	$151.055	$151.06	$151.05	$151.10
Purchase #3	$91.70	8.463%	$99.4606	$99.46	$99.45	$99.50
Purchase #4	$249.42	5.429%	$262.961	$262.96	$262.95	$263.00
Purchase #5	$187.69	11.689%	$209.6291	$209.63	$209.65	$209.60
Purchase #6	$225.81	3.493%	$233.6975	$233.70	$233.70	$233.70
Purchase #7	$36.78	12.371%	$41.3301	$41.33	$41.35	$41.30
7 purchase totals =	$1,171.06		$1,271.5290	$1,271.54	$1,271.55	$1,271.60