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	$228.54	13.356%	$259.0638	$259.06	$259.05	$259.10
Purchase #2	$167.96	13.456%	$190.5607	$190.56	$190.55	$190.60
Purchase #3	$241.44	13.211%	$273.3366	$273.34	$273.35	$273.30
Purchase #4	$12.43	11.256%	$13.8291	$13.83	$13.85	$13.80
Purchase #5	$190.57	8.547%	$206.858	$206.86	$206.85	$206.90
Purchase #6	$127.88	6.400%	$136.0643	$136.06	$136.05	$136.10
Purchase #7	$185.81	7.862%	$200.4184	$200.42	$200.40	$200.40
7 purchase totals =	$1,154.63		$1,280.1309	$1,280.13	$1,280.10	$1,280.20