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	$127.60	11.708%	$142.5394	$142.54	$142.55	$142.50
Purchase #2	$159.28	3.370%	$164.6477	$164.65	$164.65	$164.60
Purchase #3	$161.90	8.152%	$175.0981	$175.10	$175.10	$175.10
Purchase #4	$136.70	10.125%	$150.5409	$150.54	$150.55	$150.50
Purchase #5	$44.28	3.360%	$45.7678	$45.77	$45.75	$45.80
Purchase #6	$154.64	4.391%	$161.4302	$161.43	$161.45	$161.40
Purchase #7	$29.76	6.194%	$31.6033	$31.60	$31.60	$31.60
7 purchase totals =	$814.16		$871.6274	$871.63	$871.65	$871.50