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	$183.29	4.688%	$191.8826	$191.88	$191.90	$191.90
Purchase #2	$26.92	3.509%	$27.8646	$27.86	$27.85	$27.90
Purchase #3	$172.78	10.214%	$190.4277	$190.43	$190.45	$190.40
Purchase #4	$216.54	10.861%	$240.0584	$240.06	$240.05	$240.10
Purchase #5	$144.78	11.590%	$161.56	$161.56	$161.55	$161.60
Purchase #6	$241.58	7.196%	$258.9641	$258.96	$258.95	$259.00
Purchase #7	$146.40	13.733%	$166.5051	$166.51	$166.50	$166.50
7 purchase totals =	$1,132.29		$1,237.2625	$1,237.26	$1,237.25	$1,237.40