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	$40.25	13.124%	$45.5324	$45.53	$45.55	$45.50
Purchase #2	$46.51	10.719%	$51.4954	$51.50	$51.50	$51.50
Purchase #3	$161.51	8.826%	$175.7649	$175.76	$175.75	$175.80
Purchase #4	$128.75	9.422%	$140.8808	$140.88	$140.90	$140.90
Purchase #5	$193.69	9.493%	$212.077	$212.08	$212.10	$212.10
Purchase #6	$179.85	6.528%	$191.5906	$191.59	$191.60	$191.60
Purchase #7	$122.89	6.292%	$130.6222	$130.62	$130.60	$130.60
7 purchase totals =	$873.45		$947.9633	$947.96	$948.00	$948.00