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	$242.31	12.518%	$272.6424	$272.64	$272.65	$272.60
Purchase #2	$40.50	8.228%	$43.8323	$43.83	$43.85	$43.80
Purchase #3	$12.27	4.537%	$12.8267	$12.83	$12.85	$12.80
Purchase #4	$232.69	3.704%	$241.3088	$241.31	$241.30	$241.30
Purchase #5	$59.29	10.542%	$65.5404	$65.54	$65.55	$65.50
Purchase #6	$153.86	3.485%	$159.222	$159.22	$159.20	$159.20
Purchase #7	$79.41	3.330%	$82.0544	$82.05	$82.05	$82.10
7 purchase totals =	$820.33		$877.4270	$877.42	$877.45	$877.30