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	$239.79	9.215%	$261.8866	$261.89	$261.90	$261.90
Purchase #2	$44.29	6.621%	$47.2224	$47.22	$47.20	$47.20
Purchase #3	$142.31	6.662%	$151.7907	$151.79	$151.80	$151.80
Purchase #4	$105.86	10.733%	$117.222	$117.22	$117.20	$117.20
Purchase #5	$159.29	11.864%	$178.1882	$178.19	$178.20	$178.20
Purchase #6	$42.50	6.765%	$45.3751	$45.38	$45.40	$45.40
Purchase #7	$52.53	3.448%	$54.3412	$54.34	$54.35	$54.30
7 purchase totals =	$786.57		$856.0262	$856.03	$856.05	$856.00