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	$249.65	12.356%	$280.4968	$280.50	$280.50	$280.50
Purchase #2	$81.63	7.400%	$87.6706	$87.67	$87.65	$87.70
Purchase #3	$66.44	6.326%	$70.643	$70.64	$70.65	$70.60
Purchase #4	$250.42	9.488%	$274.1798	$274.18	$274.20	$274.20
Purchase #5	$80.68	12.235%	$90.5512	$90.55	$90.55	$90.60
Purchase #6	$184.35	10.275%	$203.292	$203.29	$203.30	$203.30
Purchase #7	$12.27	6.243%	$13.036	$13.04	$13.05	$13.00
7 purchase totals =	$925.44		$1,019.8694	$1,019.87	$1,019.90	$1,019.90