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	$38.58	10.823%	$42.7555	$42.76	$42.75	$42.80
Purchase #2	$198.84	6.546%	$211.8561	$211.86	$211.85	$211.90
Purchase #3	$122.92	3.854%	$127.6573	$127.66	$127.65	$127.70
Purchase #4	$244.90	11.374%	$272.7549	$272.75	$272.75	$272.80
Purchase #5	$154.64	6.218%	$164.2555	$164.26	$164.25	$164.30
Purchase #6	$152.82	10.733%	$169.2222	$169.22	$169.20	$169.20
Purchase #7	$230.55	13.250%	$261.0979	$261.10	$261.10	$261.10
7 purchase totals =	$1,143.25		$1,249.5994	$1,249.61	$1,249.55	$1,249.80